I've only just joined having transferred from ee, and part of the reason for choosing id is due to this feature. Wifi calling worked fine on ee but the option disappeared as soon as I inserted the id sim which is incredibly frustrating!
Best answer by Kevin
Was the phone originally from EE (on a 24 month contract)? I ask because a similar scenario like this came from an ex-EE customer not too long ago and it seems as though EE lock out certain features on handsets sold through them to only work when used in conjunction with EE SIM's which is a shame for since unlocked devices.
If you have access to any other network SIM's in your household/ from friends etc, then you could try using their SIM in your phone to find out for sure if it is in fact a case of your S7 only being fully functional when used with EE SIM's.
If you tried the iD Mobile SIM in another SIM-Free handset that we support WiFi calling with, then we'd expect you'll have no problems there. Though please let us know how you get on with either of the above 2 tests.