I have just resolved with a workaround a frustrating iPhone 5 cellular data service glitch on returning to Australia and putting back my Telstra Post-Paid NanoSim Card after using an O2 prepaid one in Germany. I was getting an alert whenever I tried to access the internet outside of Wi-Fi range: Could not activate cellular data service. You are not subscribed to a cellular data service.
In Settings | General just above Reset at the bottom, I found I had Profiles – an entry that is not seen normally on a Telstra iPhone 5 – I guess they have the equivalent on the SIM card? This was apparently blocking access/authorisation of Telstra codes on the SIM card because there were profiles present but no configuration profile for Telstra, just three left over from the O2 SIM card initialisation. Reset Network Settings does not clear these and they get backed up and restored by iTunes. The system should check the SIM card first for authorisation to access cellular data not the profiles if any are there. Anyway, the workaround to the alert “Could not activate cellular data service; you are not subscribed to a cellular data service” was simply to delete the Configuration Profile. It was not necessary to delete the IOS Team Provisioning profiles stating the service duration below that. Of course this means when I am next in Germany, I can’t just simply put their sim card back without some procedure to restore the configuration profile they require but that is a small inconvenience compared to loss of LTE data back in Australia.
Apple technical support had patiently lead me through a network settings reset then a long backup and two stage restore process (factory then data) that did not eliminate the problem. They escalated the problem for me two levels but in the meantime I found this workaround once I noticed the profiles were present. Another Telstra iPhone 5 here had no mention of profiles in its settings to convince me I could delete it.
Thought I would post this to help anyone else experiencing similar trouble.