I am using IPhone 4S from last few months now. I got the same problem, I even I updated my firmware.
I can't end my call and it keeps on hanging at "call ending" status and can't go through into "call ended" status. When the above issue happened, I tried to use other mobile phone to call and sms my IPhone and It is ringing but my IPhone does not detect any incoming call , also not receive sms even the sms is successfully delivered. But I don't notice any "no service" with my iPhone signal. My phone’s reception is ok. I was advised by the Apple Technician to try "reset all setting" or do the firmware restoration to determine whether is software issue or not. If still happen, then try to replace a new sim card. If still happen again, then for sure it is the hardware issue and you should claim for hardware warranty to replace a new IPhone 4.