I have a Samsung phone purchased in 2013 and connected to 2 Degrees, which worked perfectly for about 2 years. Since then at random times it drops me off the network - no sending or receiving texts or phone calls, and no internet connection. The phone still shows good coverage (4 or 5 bars) and there is no error message except "failed" a long time after trying to send a text. This can happen when just sitting at home or at work (central Wellington) or while travelling through the country - there is no discernible pattern.
The only way to reconnect is to take the battery out - just switching power off and on again does not fix the problem.
Is this a 2 Degrees problem or a problem with the phone?