I upgraded to 4G with O2 a few months ago. While the 4G signal has been good around the outskirts of Newcastle, it has been pretty poor in the city centre. I rarely get a 4G signal. Sometimes can't even get 3G. I have the 5s. After complaining to O2 a few times and the implied response being that I was either imagining things or there was something wrong with my phone, they have now acknowledged a problem in the NE1 area. This confirmed my suspicions, since it was always the same location that the signal dropped off and this happened even when walking around, so the phone would have had plenty of opportunity to lock onto signals from different cells. So, if you find that you have 4G black spots where you would expect a good signal, be sure to complain & be persistent. Don't allow them to fob you off. Given their cheeky price rise recently, make them work for their money!