works fine on mine....i suggest you are on a ****e network, or on only 2G where you are. that's what usually causes this.
I guess they suggested this because it sounds like your network hasn't figured out how to route calls properly on their network when data is active, and they dump it straight to voicemail when there is a data connection active.
not the phone's fault, the phone won't even know that the call has been missed, the network simply does not route the call through and sends it to voicemail instead.
i had this on O2 a while ago. went to t-mobile (who knew how to set up their network properly for data) and never had this issue since when i am on 3G coverage. if i'm on 2G signal and have active data then yes, i miss calls. but that's how 2G networks operate.
it's truly shocking how many networks out there have absolutely no idea how to set up their networks properly for data!
see I'm tmobile uk and on newest firmware from tmobile and in edinburgh I'm mostly covered by hsdpa/3g yet I get so many people telling me they cannot reach me! As recently as yesterday I was sitting in my office, steady 3g connection, phone on the desk and I'm receiving email from a friend - "phone me"... wtf!! Turns out he tried to call me 5 times and sent txt, none came through, only half an hour later I got text from him and text from the voicemail I had 5 missed calls!!!
I'm slowly fed up with this, never had this on any other network or phone...
Will Modaco rom contain different RADIO and would that help?