Yes, the Quectel EC25-EUX supports VoLTE natively on the modem baseband, and from the board's perspective the audio path is identical: the modem handles the IMS/SIP registration and AMR codec internally and outputs standard 1.8V PCM digital audio to the RP2040 whether the call is over VoLTE or 2G/3G fallback.

I put that caveat in the README because VoLTE support in practice depends on carrier whitelisting and having the right carrier MBN profile loaded on the Quectel module (AT+QMBNCFG), not on the rest of the PCB. Here in Europe, 2G/3G is still up for a few more years, and major carriers have MBN profiles in the standard EC25-EUX firmware, so testing both VoLTE registration and CSFB fallback will be part of bring-up when the board lands.