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github-actions[bot] edited this page Aug 4, 2026 · 1 revision

Supported Hardware

At a glance

Hardware Circuit-switched calls VoWiFi VoLTE
Quectel EC20 ✅ ✅ ✅
Quectel EC200 / EC200U ❌ (no audio output) ✅ ✅
PC/SC card reader (e.g. OmniKey AG 3x21) ❌ ✅ ❌
  • Circuit-switched — classic GSM voice; the modem answers the call and sends audio over USB.
  • VoWiFi — Wi-Fi Calling, over an IPsec tunnel to the carrier.
  • VoLTE — voice over the modem's LTE data connection.

A card reader has no modem or radio at all, so it can only ever provide VoWiFi (its SIM reaches the carrier over your host's own network connection, not a cellular one) — circuit-switched calls and VoLTE both need an actual modem.

This table is about how calls arrive. Where they go afterwards — an external PBX, or an IP phone registered directly to the bridge ([sip_server].enabled) — is device-independent: every mode above works with either. See architecture.md.

Quectel EC20

The default choice — works for all three modes on the same device. See Setting up a modem below.

Quectel EC200 / EC200U

Same setup as the EC20, minus the USB-audio step (this model has no audio output, so it's always used for VoWiFi/VoLTE, never circuit-switched calls).

PC/SC card reader (OmniKey AG 3x21 and similar)

Lets a VoWiFi line's SIM sit in a card reader instead of a modem — useful if you'd rather not dedicate a whole modem to one line, or don't have one free. Setup: docs/omnikey-pcsc-vowifi.md.

Setting up a modem

One-time preparation — do this before the first run.

1. Host prerequisites

  • The modem should appear as /dev/ttyUSB* (check with dmesg | grep ttyUSB) — the option/qcserial kernel modules that provide this are normally auto-loaded.
  • If running outside Docker, add your user to the dialout and audio groups: sudo usermod -aG dialout,audio $USER.

2. Disable ModemManager — it probes serial ports and corrupts AT sessions:

sudo systemctl stop ModemManager
sudo systemctl disable ModemManager

3. Enable USB audio (EC20 only — needed for circuit-switched calls):

minicom -D /dev/ttyUSB2 -b 115200

AT+QCFG="USBCFG",0x2C7C,0x0125,1,1,1,1,1,0,1   # enable UAC
AT+CFUN=1,1                                     # reboot the module

After it reconnects, confirm with arecord -l / aplay -l — you should see a card named "Android". Repeat for each module; the setting persists across reboots.

4. VoLTE (optional, per carrier) — some modems ship with VoLTE locked off. If calls aren't connecting over LTE, see the VoLTE unlock guide.

Next steps

  • Deploy the bridge — see the Quick Start.
  • Manage modems at runtime with card list / restart / set-mode — see operations.md.

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