VoLTE, Wi-Fi Calling and the 3G Shutdown: What It Means for GSM Gateways

As operators switch off 2G and 3G, mobile voice moves to [VoLTE](/glossary/volte) (voice over 4G, delivered through the [IMS](/glossary/ims) core) and [Wi-Fi calling](/glossary/vowifi). Any GSM gateway whose radio cannot make VoLTE calls on your carrier stops working when the older network goes. Current smartphones already support VoLTE, Wi-Fi calling and HD voice, which makes them a practical gateway radio.

This article explains the network changes, what they mean for each type of gateway, and what to check before you buy or replace equipment.

The 2G and 3G sunsets

Operators retire older networks to reuse their spectrum for 4G and 5G. The timing differs by country and operator, but the direction is the same everywhere:

• United States: the major carriers shut down their 3G networks during 2022, following earlier 2G closures. Phones and devices without VoLTE support approved by the carrier lost the ability to make calls on those networks.
• Europe: many operators retired 3G between 2020 and 2025, often keeping 2G a little longer for machine-to-machine devices. The UK government and operators have agreed that 2G and 3G will be switched off by 2033, with 3G largely gone already.
• Australia: the major operators closed their 3G networks in 2024, and some older 4G phones that did not support VoLTE correctly — including for emergency calls — were blocked from the networks.
• Elsewhere: operators in Asia, the Middle East and Africa are following the same path at different speeds; 2G often survives longer where it still carries a lot of traffic.

What VoLTE and IMS actually are

In 2G and 3G, voice uses dedicated circuit-switched channels. 4G LTE has no circuit-switched voice at all: it is an all-IP network. Voice over LTE carries calls as IP packets, controlled by the IP Multimedia Subsystem (IMS) — a 3GPP architecture that uses SIP for signalling, much like the VoIP systems it will ultimately connect to.

The GSMA’s IR.92 profile defines the minimum feature set a VoLTE device and network must support, which is what makes phones and networks from different vendors interwork. Before VoLTE was widespread, 4G phones used circuit-switched fallback (CSFB), dropping back to 3G or 2G for each call. When those networks disappear, CSFB has nowhere to fall back to — which is why a 4G device without VoLTE can lose voice entirely.

Voice over 5G (VoNR) builds on the same IMS core. For gateway purposes, the practical question is the same: will this device make IMS voice calls on this carrier?

Wi-Fi calling (VoWiFi)

Wi-Fi calling carries the same IMS voice service over any internet connection. The phone builds an encrypted IPsec tunnel (set up with IKEv2) to the operator’s ePDG gateway, then registers with IMS through it, exactly as it would over LTE. The call is still a normal call on the subscriber’s number, billed and routed by the operator; the GSMA’s IR.51 profile covers it.

For gateway sites, Wi-Fi calling can help where indoor mobile coverage is weak, such as basements, steel-framed buildings and rural locations. Two cautions apply: carriers only offer it on some plans and devices, and quality now depends on the site’s internet link as well as the phone. On some phones Wi-Fi calling also depends on VoLTE being enabled, so treat the two as a pair.

Why 3G USB dongle gateways fail

For years, a popular low-cost gateway was a Linux server running Asterisk with a stack of USB modems, typically using the chan_dongle driver. That approach is ending for several reasons:

• Voice ran over 3G. The voice-capable dongles most people used were 3G devices. On a network with no 3G, they cannot make calls at all.
• VoLTE is harder than it looks. VoLTE needs a full IMS client, operator-specific configuration and, on many carriers, device certification. Most USB modems are built for data and do not provide VoLTE voice to the host.
• Carrier allow-lists. Several carriers only permit VoLTE on devices they have approved; uncertified modules can be refused service.
• Ageing software. The open-source drivers were written for specific modem firmware and are not a path to VoLTE.

Hardware GSM gateways face a milder version of the same problem. Modern chassis ship with 4G modules and VoLTE support, but whether a given model works on your carrier depends on module firmware and the carrier’s approval list. Ask vendors for evidence of VoLTE calls on your specific networks.

Why smartphones are good VoLTE endpoints

A current smartphone sold for your market is exactly the kind of device carriers certify for VoLTE. It receives the operator’s IMS configuration automatically, supports Wi-Fi calling where the plan allows, and is updated by the manufacturer as networks change. That is why phone-based gateways side-step most of the 3G-sunset problem: the radio in the gateway is the same kind of device the network is designed for.

Phones still need the operational care described in can an Android phone be a GSM gateway? — power, heat, a reliable audio path and central monitoring — but they take the network-compatibility question off the table.

HD voice from the mobile network to your PBX

VoLTE calls between compatible phones typically use AMR-WB (ITU-T G.722.2), a wideband codec with 16 kHz sampling, or 3GPP’s newer EVS codec. That is “HD voice”: noticeably clearer than the 8 kHz narrowband audio of classic telephony.

A gateway preserves that quality only if every link after the radio is wideband too. If the audio path from the phone is narrowband — an analogue cable into an 8 kHz sound card, or Bluetooth hands-free using the CVSD codec — the HD is lost before the call reaches your trunk. On the SIP side, G.711 is narrowband by definition; G.722 or Opus carry wideband audio to the PBX and handsets.

The GSMCalls Smart Bridge was built for this: a microcontroller on the phone’s USB-C port with the GSMCalls app streaming digital wideband G.722 audio to the cloud, with no PC and no analogue stage. See GSM gateway without a PC.

Checklist for gateway buyers in 2026

1. List every carrier you use and its 2G/3G shutdown dates.
2. Confirm VoLTE works on each of those carriers with the exact device or module — ideally with a test call, not a spec sheet.
3. Decide whether you need Wi-Fi calling for poor-coverage sites, and check that your plans include it.
4. Decide whether HD voice matters to you, and check that the audio path and SIP codec are wideband end to end.
5. Plan device replacement as networks change: phones can be swapped like-for-like; chassis modules depend on the vendor.
6. Keep your use within carrier terms and local rules — see our acceptable use policy.

GSMCalls runs on current VoLTE-capable phones and manages them from one cloud GSM gateway platform, with standard SIP trunks to your PBX. For the fundamentals, read What Is a GSM Gateway?; for costs, see pricing from $100 per month for 10 phones; or book a demo.