Sorry to bump an old thread, but I'm currently having the exact same issue with my iPhone 5s. I'm with Starhub in Singapore.
There are 2 issues:
- When I turn airplane mode off and on, the phone does not connect to mobile data. This was fixed by selecting the carrier manually.
- When I walk out of a wifi area, the phone does not connect back to 3G/4G. I need to restart the phone to make it work. This does not happen all the time, but happens at least once per day. It doesn't happen on most weekends though. Very strange.
When I put another sim card (from the same carrier or another carrier) there are no issues whatsoever. When I test my sim on another phone or on my iPad 2, no issue either.
So far Starhub has no idea what's going on, and the company that handles support for Apple here keeps saying it's a network issue.
Anyone else experiencing this issue on the iPhone 5s?