Quite the same title and the same problem from the other thread: /t5/Nokia-with-Windows-Phone/Can-t-end-a-call-in-l
I opened this one also to collect feedback from the 710's owner.
It's really annoying and quite disappointing that a very nice phone like this is simply missing the BASICS of a phone.
This is my 4th device and this is the only one where this problem is happening.
I really hope that some solution will come up fast.