Wholesale VoIP & Call Termination Explained

[Wholesale VoIP](/glossary/wholesale-voip) is the carrier-to-carrier market in which operators buy and sell capacity to deliver each other’s calls. Call termination delivers a call to the network serving the called number; call origination collects calls from callers onto a network. Routes are priced per minute by destination and judged by ASR, ACD and PDD.

This article explains how the lawful wholesale market works, what the jargon means, and what people mean by “GSM termination” and “Android termination” — including why unlicensed termination through SIM cards is illegal in most countries.

How the wholesale voice market works

No retail phone company has a direct connection to every network in the world. When a customer in one country calls a mobile number in another, the call usually passes through a chain of operators:

1. The originating provider — the caller’s phone company, PBX provider or VoIP service — receives the call.
2. It hands the call to one or more wholesale (transit) carriers, chosen by price and quality for that destination.
3. The last carrier in the chain delivers the call to the terminating operator — the network that serves the called number — over a licensed interconnect.
4. The terminating operator connects the call to its subscriber and charges the carrier that handed it over a termination rate.

Money flows in the opposite direction to the call: each party pays the next one for carrying it onward. Termination rates are a regulated subject in many regions — the EU, for example, sets single maximum fixed and mobile termination rates (the “Eurorates”, Delegated Regulation (EU) 2021/654) — while international termination rates into many other countries are set commercially or by national regulators.

Origination vs termination

A business SIP trunk usually bundles both: DIDs for inbound calls and outbound termination to the public network, bought from a retail or wholesale provider.

A–Z routes, rate decks and billing increments

Wholesale carriers publish rate decks: spreadsheets listing every destination they sell, keyed by dialling prefix. An “A–Z” deck covers every country and network; a carrier may also sell individual destinations it specialises in. A typical deck row contains:

• Prefix / code: the leading digits that identify the destination (for example a country code plus a mobile network code).
• Destination name: such as “United Kingdom – Mobile”.
• Rate: price per minute, often to four or more decimal places.
• Billing increment: how duration is rounded — 60/60 bills whole minutes, 1/1 bills per second, 30/6 bills a 30-second minimum then 6-second steps.
• Effective date: when a new rate applies. Rate changes are normally notified in advance.

Routes are also sold in quality classes. A CLI route delivers the caller’s number (caller ID) intact; routes that do not preserve CLI are cheaper and are frequently a sign that traffic is being delivered through bypass rather than a licensed interconnect.

Measuring route quality: ASR, ACD and PDD

Because a wholesale call passes through several networks, carriers constantly measure the routes they buy. The core metrics come straight from call detail records:

Carriers also watch for false answer supervision (FAS) — a route signalling “answered” while the caller still hears ringing or a recording, so the call is billed although nobody picked up. FAS is a recognised form of wholesale fraud and a reason carriers audit suppliers with test calls.

Class 4 switching and wholesale billing

Wholesale traffic is handled by a Class 4 softswitch: a carrier-grade softswitch that routes calls between networks rather than serving end users (that is the job of a Class 5 softswitch or PBX). A Class 4 switch typically provides:

• Least-cost and quality-based routing: choosing, per prefix, the cheapest supplier that meets quality targets, with automatic failover to the next route.
• Number normalisation: converting numbers to a consistent format such as E.164 before routing.
• Capacity and fraud controls: per-customer channel limits, credit limits and blocking of high-risk destinations.
• Rating and CDRs: pricing every call against the right rate deck.

Telecom billing then turns rated CDRs into invoices. Carriers reconcile their CDRs against each partner’s every cycle; differences in rounding, time zones or answer detection become disputes, which is why accurate answer times and consistent billing increments matter so much.

What “GSM termination” and “Android termination” mean

Search for wholesale VoIP and you will find sellers offering “GSM termination”, “SIM termination” or “Android termination”. In that part of the market, the terms describe delivering international calls into a country through local SIM cards — in a SIM box, a multi-SIM gateway or a rack of phones — so that each call reaches the called party as a local mobile call.

The call skips the licensed international interconnect, and the terminating operator receives only a local retail tariff instead of the international termination rate it is entitled to. This is interconnect bypass, commonly called SIM-box fraud. The caller’s number is usually replaced with the local SIM’s number, and quality suffers.

Lawful ways to use mobile gateways

Mobile gateways have plenty of legitimate uses that have nothing to do with wholesale termination. They centre on an organisation using its own lines, for its own calls, under its carrier’s terms:

• Enterprise outbound calling from SIMs on business plans that permit the use — for example, a PBX reaching mobile customers from a local mobile number.
• Inbound mobile numbers delivered into a PBX or contact centre, so customers can call a familiar mobile number.
• Call centres routing callbacks over their own local lines, with genuine caller ID.
• Network testing and monitoring with the knowledge of the operators involved.
• Failover and remote sites where fixed lines are unavailable or down.

If you need to reach destinations at scale, buy termination from licensed carriers or a wholesale SIP trunk provider, and keep your mobile gateways for the lines you own. GSMCalls works with your PBX alongside those trunks — see the cloud GSM gateway and multi-site GSM gateway pages.

Checklist: buying wholesale termination responsibly

1. Deal with carriers that can show their licences and sign a proper interconnect or service agreement.
2. Require CLI delivery and, in the US, compliance with the FCC’s STIR/SHAKEN caller-ID authentication rules.
3. Treat rates below the destination’s official termination rate as a red flag: they are rarely possible without bypass.
4. Monitor ASR, ACD and PDD per route and test-call suppliers regularly.
5. Keep CDRs and contracts for as long as your regulators and disputes require.

Want to connect mobile lines to your phone system the lawful way? See pricing or book a demo with our engineers.