The mobile network drops out, seemingly at random, a few times a day. The provider says there's nothing wrong on their end; I live in a city where reception is astoundingly good. Every time I have to completely turn off the phone; when restarted the network is there without problem. What could be the cause of this? Obviously it is inside the phone, and not a faulty network. PS I have already done a complete reset, but the same problem returned after a day or two.