I have VM mobile, samsung s6, I mainly use it for browsing ect but the odd occaisions i use it for making calls usually ends up with the following issues:
1: Make call, other person can't hear me or i can't hear them.
2: Recieve call,other person can't hear me or i can't hear them.
3: Make call nothing happens, end call, make call nothing happens.
4: During call, call drops.
This has been the norm for the little i actually use the phone. This will also happen with my partners phone who is on EE direct with same phone.
Seems to happen more within Clacton area. Can't get through to customer service at present to find out if there and faults,(again as i have phoned over the past few years and seem to be alot of issue related).