Upgraded 3GS to ios 6, went overseas using different SIM, when returned and put one of the coolest iphone 4 cases and the usual SIM back in, incoming SMS no longer working. Outgoing SMS OK. Phone network provider says number OK. Tried usual on/off etc with no success. Any tips?
Did you try taking out the battery and the sim and holding the reset button down for 10-15 seconds?