Cannot make calls, says 'call ended' immidiately

Phone worked fine, changed the rear housing and screen and now when i try to make a call, it says 'call ended' before it even dials. When i try again, it wont even attempt to call, when i click a contact it just wont even attempt.

Have tried restoring phone, have tried replacing the dock connecter (which i believe has some sort of antenna in it) and now i am unsure of what to do. I have been told it could be software, but I have restored it to factory settings and set it up as a brand new iPhone and the problem still persists so i am unsure.

Any help would be really appreciated.

Thanks

Jacob