When the phone goes from a non signal area to an area where I know it should have signal, it still show 'No Service' in the top left corner. I have to turn the phone off and on again or make a call to bring back the signal. My phone will not accept calls when it's shows 'No Service' in the area where I know it should have signal. My partners 4S was the same until she installed IOS6. Her phone seems to be ok at the moment. This fault is really frustrating and orange my network provider have been no help to date!!
Any one else getting this issue??
I've found a very effective solution for my iphone5 running ios6.1.3.
go to settings>Carrier. Change it to manual and wait for a while till it loads the list of providers and select the network of the inserted SIM card. Now, turn the airplane mode on and then off. Leave the carrier selection to manual. You will now have better network reception. It perfectly worked for me.