Luxembourg: SIP providers and connecting a number to the PBX

This page continues the general guide to connecting a provider's number to the PBX: that page covers what is the same for every carrier — the two trunk modes, what to ask the provider, what to enter in the form, network requirements and how to test the link. Here is the Luxembourg part: who sells a number with a SIP trunk in the country, what that carrier issues and what of it goes into Telephony → "Trunks and connections" → "Add provider".

The data was collected on 9 September 2026 from carrier documentation and materials of the regulator ILR; links are in the "Sources" section.

In short#

• You can buy a number with a SIP trunk in Luxembourg. No licence is needed: the telecom service is sold by a Luxembourg carrier, and it is the carrier — not you — who notifies the regulator (ILR) of its activity.
• The main candidate is Mixvoip (formerly VoipGATE and Crossing Telecom). The only local carrier that publicly states both authorization modes — username/password and IP address — works over regular internet, and lists Asterisk among its certified systems. Trunk pricing starts at €3.80 per channel per month, a Luxembourg number costs €1.60/month.
• The second candidate is Luxembourg Online, if the venue already buys internet from them: the product is named plainly "SIP Trunking" and is built around authorization by a dedicated IP address.
• The main local pitfall is the numbering itself. Luxembourg has a closed variable-length numbering plan: a fixed-line national number can be anywhere from 5 to 10 digits, with no area codes and no national prefix. A short number (5–6 digits) is a weak key for our line matching, which checks the last seven digits — and the country's classic carrier scheme, "racine" (root number) plus extension, requires the line to be entered as the full number, not the root, or the incoming call will never find it.
• The incumbent's POST/DEEP trunk does not connect to a cloud PBX. Their "SIP Trunk" runs over the carrier's own dedicated line bypassing the public internet, with the interconnect box available for rent only, on the client's premises — for our PBX in the cloud that is a "no", whatever the product is called.
• A legal quirk — numbers are for end users only. In 2026 the regulator ILR fined an international number aggregator €25,000 specifically for passing Luxembourg numbers on to third parties. For a venue that buys a number as an end user from a notified carrier this is not a blocker, but it is a reason not to shop for "a cheaper number through a reseller".

Numbers in Luxembourg#

• Country code — +352. There is no national prefix and no area codes: the numbering plan is closed, and every digit dialed inside the country is also the international number.
• The length of a national fixed-line number is 5 to 10 digits (depends on the range and the carrier it was assigned to). Mobile numbers are 9 digits (ranges 62x, 65x, 66x, 67x, 68x, 69x). Premium-rate numbers (800, 801, 900, 901, 905) are 8 digits.
• Dialing. Inside the country it is just the number, no trunk prefix at all. Abroad — 00 + country code. In E.164 a Luxembourg number is +352 plus the same 5–10 digits, no leading zero.
• How a carrier assigns a number — "racine" (root) plus extension. A classic installation in this country holds a root number (6 or 8 digits — a carrier is allowed to mix lengths on the same site) and appends extensions to the right: the incoming number is the root plus the extension tail, not a standalone number.

On the "Lines" tab a number can be entered in any format: the PBX matches by the last seven digits. For Luxembourg this creates two separate problems:

1. A short number (5–6 digits) is a weak key. A line entered as 27123 (5 digits) will match any incoming call ending in 27123 — including someone else's longer or mobile number. On a trunk with a single number this does not matter; on a trunk with several it is the source of "the call landed on the wrong line".
2. A line cannot be set up on the "racine". The incoming DID is the root plus the extension, with the root sitting to the left of it; suffix matching will never find the root as a standalone number. Enter lines as full numbers (DDI), never as the "racine".

Numbers of 9–10 digits and numbers already in full international format are not affected — a seven-digit tail is enough to tell them apart within the same root.

Who sells a number with a SIP trunk#

The first three rows are carriers whose product and authorization mode are known in advance: their cards are below. For the rest of the Luxembourg carriers parameters are issued only under contract — see the separate section.

Mixvoip#

A Luxembourg carrier since 2008 (today's brand combines the former VoipGATE and Crossing Telecom — both domains now lead to the Mixvoip site and branding), by its own account the second-largest carrier by share of fixed voice traffic in the country, with direct interconnects to major local carriers.

There is no "pay by card, get a trunk" self-service — connection goes through a request. Pricing is public though: SIP trunk €3.80 / €6.60 / €9.60 per channel per month (Standard / Business / Advanced tiers), a Luxembourg number €1.60/month, a block of 10 — €3.10, a block of 100 — €10.20, setup €16.20; porting and emergency calling for Luxembourg numbers are available.

What to enter in the admin panel

What to set up with the provider: order a trunk with the needed number of channels → choose the mode (account, or IP allowlist) → attach numbers/racine to the trunk → confirm how the DID arrives (full number or national digits) → enable your own caller ID ("show as") — CLIP no screening is stated as a standard feature of the trunk.

Pitfalls ⚠️ According to an independent interoperability test (from 2021, with no newer data disproving it), Mixvoip does not support in-band DTMF as RTP events (RFC 2833/4733) and does not support SIP INFO — our pjsip stack sends RFC 4733 by default, and this is the first thing to check on a live trunk (IVR and "press 1" will otherwise not work); fixed by switching the dial tone mode to inband on the PBX side. The trunk codec is only G.711A (exactly our alaw), SRTP and T.38 fax do not work — not critical for us. Registering two SIP interfaces on one account is allowed (load balancing), but there is no automatic failover if one node goes down — calls may fail for up to 2 minutes. The flat rate on long-distance directions and "anti-fraud protection" require Mixvoip's internet and PBX certification — a cloud PBX does not meet that condition, so minutes are billed at the regular price.

Source: SIP Trunk · SIP trunk Luxembourg · Phone numbers — 09.09.2026.

Luxembourg Online#

A carrier with its own network across 150+ sites in the country, more than 30 years in the market. The product for your own PBX is named plainly — "SIP Trunking" — and is aimed at those who host their own IPBX and want to configure everything themselves, keeping their own switch and phones. The carrier handles setup and configuration of the subscription itself, at no extra charge.

What to enter in the admin panel

What to set up with the provider: give the carrier the static IP of our dedicated PBX for the allowlist → ask in writing for the six fields of our form (in case the carrier does issue an account) and the DID format → confirm that RTP will land on our address in the usual UDP port range → confirm whether emergency calls (112) are delivered.

Source: SIP Trunking — 09.09.2026.

Visual Online#

A Luxembourg carrier (part of the POST group), more than 30 years in the market. The product is called "SIP-Trunk for IP-PBX" — per the carrier's own description, "from a small business all the way up to a large corporation". A separate cloud PBX is also sold, but here we are interested in the trunk to your own system. Parameters, pricing and the authorization mode are not published on the site — everything goes through the sales team.

What to enter in the admin panel

What to set up with the provider: ask directly whether the trunk runs over the public internet or, like POST (see below), over a dedicated line — the carrier is in the same group; confirm G.711 support and IP-auth mode; confirm the DID format.

Pitfalls ⚠️ Almost all the technical detail here is a default assumption, not a documented fact: before planning a connection date, wait for a written answer from the manager on every field of the form.

Source: SIP-Trunk — 09.09.2026.

Contract-only carriers and POST/DEEP#

For these carriers, the product either exists only "by contract" with no public parameters, or it simply does not fit our cloud PBX at all. There is no "what to enter" table here — ask for parameters using the checklist from "What to ask the provider" and enter them in the same form as for the rest.

POST Luxembourg / DEEP Telecom#

The country's incumbent; business telecom is sold under the DEEP brand. Three trunk products — SIP Trunk Business, SIP Trunk on ConnectedOffice, SIP Trunk Corporate — share one trait: the connection runs over POST's own dedicated line, bypassing the public internet, and the interconnect box (SBC Gateway) is available for rent only, on the client's premises. Our PBX lives in the cloud and is not part of POST's access network — the trunk physically cannot reach it, no matter what it is called.

Useful to know from the carrier's public FAQ: the subscription requires your own PBX with an IP/PRI/BRI interface; 2–60 channels (more on request); activation takes 4–6 weeks; minimum contract term 1 year; a mix of 6- and 8-digit roots ("racine") is allowed on the same installation, with the number of roots equal to the number of channels; CLIP no screening is supported but not guaranteed on every interconnect.

If a venue is already on POST, the sensible move is not a trunk but a number port (1 business day, see below) to a carrier that offers an internet-based trunk: Mixvoip or Luxembourg Online.

International providers with Luxembourg numbers#

A few international providers sell Luxembourg numbers; their trunk parameters are the same across countries — take them from the provider's card in the admin catalog or from the "Add provider" section, here is only the Luxembourg-specific part:

• DIDWW states local SIP trunking in Luxembourg with guaranteed caller ID, local dialing and access to emergency services; both our modes are supported (DIGEST registration and IP authentication). ⚠️ Country caveat: on 27.03.2026 the regulator ILR fined DIDWW Ireland Limited €25,000 and banned it from passing Luxembourg numbers to anyone other than end users. For a venue buying a number as an end user this is not a ban, but it is a reason to make sure the number is registered to you, not "through a reseller".
• Telnyx sells Luxembourg numbers, but the requirements are published line by line and are strict: local-type numbers require a company registration certificate, an address in Luxembourg confirmed no more than 3 months ago, and an explicit condition — "business use is required, private use is not allowed".
• Zadarma sells geographic, national and toll-free numbers for Luxembourg, documents are a company registration certificate or a passport with proof of address; for a geographic number the address must be in the number's own region.
• Twilio keeps a dedicated pricing page for Luxembourg SIP trunking with local numbers from a few dollars a month — unlike some neighboring markets where Twilio has no voice numbers at all.
• Common to all of them: Luxembourg geographic numbers are meant for use inside the country, and "permanent and exclusive" placement of a number on foreign carrier equipment is treated by the regulator as a breach of the allocation. The practical takeaway — for meaningful call volume take a number from a local carrier, and use an international provider as a backup route or for outbound calls.

Number porting#

• Porting is mandatory and fast. The porting obligation applies to every notified carrier; the maximum term is 1 business day for both fixed and mobile numbers, as long as the subscriber's infrastructure does not change.
• The receiving carrier initiates the port on your request; that same request also terminates the contract with the previous carrier. Porting data flows through a central database that every numbered carrier is required to connect to.
• What gets ported: geographic/fixed numbers, mobile numbers, toll-free 800 numbers — with the receiving carrier required to log the entry in the shared database. The donor carrier must hand over the required porting information within 3 business days.
• What to ask before porting: whether the whole "racine" with its extensions moves as one block (porting the root pulls the whole DID range); whether 112 and service calls go through the new trunk; whether short numbers and call forwarding rules survive.
• A number registered to a legal entity is standard practice. Local carriers contract with a Luxembourg legal entity (company register, VAT number); international providers publish their own requirements (see above) — Telnyx explicitly bans private use for local-type numbers.
• Emergency calls are tied to the address. When porting or changing the venue's address, update it with the carrier — otherwise 112 may be routed to the wrong dispatch centre.

Rules and paperwork#

If it does not work#

Country-independent causes are covered in "If calls do not go through"; checking the address and port — in "Test the connection".

Frequently asked questions#

Which carrier should I pick if nothing is connected yet?#

Mixvoip. It is the only local carrier that publicly states both REGISTER and IP-based authorization, works over regular internet, and lists Asterisk among its supported systems. Just account for the DTMF pitfall (see "If it does not work") — worth checking on the very first test day. The fallback is Luxembourg Online, if the venue already uses their internet.

Why doesn't the POST/DEEP trunk fit our cloud PBX?#

The product is designed as a dedicated line bypassing the public internet, with the interconnect hardware (SBC Gateway) rented on the client's premises. Our PBX lives in the cloud and is physically not part of POST's access network — the trunk cannot reach it, regardless of the tariff or channel count. If a venue is already on POST, it is easier to port the number to a carrier with an internet-based trunk.

Why aren't the hosts and ports of local carriers stated precisely?#

Except for Mixvoip (and even that only partly, from independent interoperability testing rather than the carrier itself), Luxembourg providers do not publish trunk parameters on their sites — they come by letter or in the customer portal after a contract is signed. Do not plan a same-hour connection without submitting a request first — leave time for correspondence with the carrier.

What are these short numbers in Luxembourg, and why do they matter for lines?#

The country has a closed, variable-length numbering plan: a fixed-line number can be 5 to 10 digits, with no area codes. Our line matching, which checks the last seven digits of a number, gives a weak key for short numbers (5–6 digits), and for the classic "racine + extension" scheme it simply does not find the root as a standalone number at all. Enter lines as full numbers (DDI), never as a "racine" — see "Numbers in Luxembourg" for details.

Can I get a Luxembourg number from an international provider instead of a local carrier?#

Technically yes — DIDWW, Telnyx, Zadarma and Twilio all sell Luxembourg numbers and support our connection modes. But the country's regulator has a recent record of fining providers for passing Luxembourg numbers to non-end-users, and document requirements from international providers are stricter than local ones (for example, Telnyx explicitly bans private use for local-type numbers). For meaningful call volume, a number from a notified local carrier is the safer choice.

Sources#

All links checked on 09.09.2026.

Regulator

• ILR — Plan national de numérotation (closed variable-length plan, no national prefixes or area codes): https://www.ilr.lu/secteurs-activites/communications-electroniques/numerotation/plan-national-numerotation/
• ILR — E.164 Number Ranges in use in Luxembourg, PDF, May 2026 (number ranges and lengths): https://www.ilr.lu/wp-content/uploads/ilr-telecom-E.164-Number-Ranges-in-use-in-Luxembourg_new.pdf
• ILR — Portabilité des numéros (1 business day porting, procedure): https://www.ilr.lu/secteurs-activites/communications-electroniques/numerotation/portabilite-numeros/
• ILR — decision ILR/T26/3 of 27.03.2026 against DIDWW Ireland Limited, PDF (€25,000 fine, ban on reselling numbers): https://www.ilr.lu/wp-content/uploads/ilr-telecom-20260327-Sanction_DIDWW.pdf

Carriers

• Mixvoip — SIP Trunk (pricing, authorization modes): https://www.mixvoip.com/sip-trunk/
• Mixvoip — SIP trunk Luxembourg (market share, interconnects): https://www.mixvoip.com/sip-trunk/luxembourg
• Mixvoip — Phone numbers (DID) coverage (number pricing): https://www.mixvoip.com/phone-numbers/
• POST / DEEP — IP telephony with your existing switchboard (three SIP Trunk products, dedicated line): https://www.deep.eu/en/accueil/services-et-solutions/telecom/collab-et-tel-fixe/telephonie-sur-ip
• POST — FAQ SIP Trunk Business, PDF (subscription conditions, racines, channels, timelines): https://www.post.lu/documents/20125/1457098/POST_FAQ_SIP_TRUNK_A4_FR.pdf
• Luxembourg Online — SIP Trunking (trunk for your own IPBX, dedicated IP): https://www.internet.lu/business/fr/pme/telephonie/sip-trunking.html
• Visual Online — SIP-Trunk (product for IP-PBX): https://business.vo.lu/en/telephony/sip-trunk/
• DIDWW — SIP Trunking Luxembourg: https://www.didww.com/voice/global-sip-trunking/Luxembourg
• Telnyx — Luxembourg DID requirements: https://support.telnyx.com/en/articles/3739502-luxembourg-did-requirements
• Zadarma — virtual phone number in Luxembourg: https://zadarma.com/en/tariffs/numbers/luxembourg/
• Twilio — SIP trunking pricing, Luxembourg: https://www.twilio.com/en-us/sip-trunking/pricing/lu

Related pages#

• Connecting a provider's number to the PBX — general steps, trunk modes, network, testing the connection.
• Setting up SIP phones — how to connect desk phones and DECT to extensions.