It might have struggled for stock of the iPhone 5s at launch, but O2 is still taking orders for the phone and selling it as and when stock arrives, as well as stocking the iPhone 5c. But a bigger problem was 4G connectivity.Initially, O2 had the 4G network up and running, but it wouldn't play nicely with Apple's latest hardware. A couple of weeks on and it seems that the problems have been ironed out.In order to get the faster speeds (presuming you have signed up to a 4G deal with O2), you need to put the SIM into the phone, check you are in a Wi-Fi zone, turn on the iPhone, follow the onscreen instructions to activate and set it up. Once the phone is activated, go to Settings, then General, then About and you'll be asked to update carrier settings. A tap on 'Update' and you are ready to go.To make up for the lack of 4G in the early days of ownership, O2 will knock £5 off your 4G bill. Which is nice.