Comfort GSM not answering but SMS is working

[caravanboy]

Re-sent

[caravanboy]

I just had need to dial-in to Comfort and again had issues with DTMF tones not being recognised by the 4G SIM module. I'd forgotten that you'd emailed me and said you also couldn't sign-in to my system either and suggested I tried a new SIM card...

So, I have just been looking at info on the main mobile network providers in the UK:

• THREE claims to have excellent 4G coverage inside and outside
  
• O2 4G coverage is 'good' (but my own mobile is on O2 and isn't always great)
  
• EE and Vodafone say they might only work outdoors in my area so I'll ignore those two.
  

All of the networks say they support VoLTE these days on their 4G connections. That is obviously essential for my latest Comfort UCM/4G module that I purchased in early 2025 (the A7608 one as it was known at the time) which has the A7608E chip.  However, The THREE network said that not all VoLTE devices will work with their network on the virtual MVNO SIM providers, I found a page on one of their virtual network providers that says that the device must support the 800MHz frequencies for VoLTE - here. However, the IMEI info website doesn't list any frequencies for my A7608E.

So, please can you tell me which frequencies the device supports?  I can then decide which alternative SIM to try.

Thanks