EG915U-EU - Voice calls failing with Iliad Italy M2M SIM - Works only with standard PDP, fails with Quectel stack

IoT Modules LTE Standard Module
1

Dear Quectel Support and Community,

I am experiencing an issue with voice calls on the EG915U-EU module (firmware EG915UEUABR03A01M08) when using Iliad Italy M2M/IoT SIM (PLMN 22250).

Hardware / Software

  • Module: EG915U-EU
  • Firmware: EG915UEUABR03A01M08
  • SIM: Iliad Italy M2M (data + SMS works perfectly, voice does not)
  • For comparison I also tested a Vodafone consumer SIM (full VoLTE support)

Problem Summary

With Iliad M2M SIM:

  • VoLTE never registers (no IMS registration).
  • When using Quectel TCP/IP stack (QICSGP + QIACT), outgoing calls fail: ATD returns OK but no ringing, timeout after ~30-40s.
  • When using standard PDP context (CGDCONT + CGACT) + network auto mode, calls work via CSFB (ringing on 2G), but data suspends during the call (+QIURC: “pdpdeact”,1).
  • Trying to create a dedicated IMS bearer (CID=2, “IPV4V6”, APN “ims” or “iliad”) always fails with +CME ERROR: 3 (operation not allowed).
  • In LTE-only mode (nwscanmode=3) → NO CARRIER + +CEER: 1,1 (unassigned number).

With Vodafone SIM (same module and firmware):

  • VoLTE works reliably with standard PDP, Quectel TCP/IP stack, and hybrid configuration.

Tests Performed

I did extensive testing with both SIMs and all common configurations:

  1. Standard PDP only → Iliad: CSFB works | Vodafone: VoLTE works
  2. Quectel TCP/IP stack only → Iliad: fails (no ring) | Vodafone: VoLTE works
  3. Hybrid (stack + dedicated IMS bearer on CID=2) → Iliad: CGACT ERROR 3 | Vodafone: VoLTE works
  4. IMS enabled/disabled, LTE-only, GSM-only, factory reset, etc.

Questions for Quectel

  1. Is there a known issue with EG915U-EU (especially revision BR03A01M08) and Iliad Italy (PLMN 22250) regarding VoLTE / CSFB?
  2. Is there a specific MBN profile, firmware update, or undocumented AT command to make VoLTE or reliable CSFB work with Iliad M2M SIMs?
  3. Why does the Quectel TCP/IP stack prevent CSFB on Iliad while it works fine on Vodafone?
  4. Is there a recommended way to have permanent TCP/SSL data (stack) + reliable voice calls on the same module with Iliad M2M SIMs?

I could verify that this issue is present with more “M2M like” SIM cards.

I can provide full logs, exact command sequences, and comparison tables if needed.

Any help, firmware recommendation, or configuration advice would be highly appreciated.