[siftrics]

Ironically, it seems that this only happens when you are within service.

Another commenter speculated that when you're out of service, the software correctly identifies that there is no tower to connect to and stops trying. But when you're in service, the code repeatedly tries to do the 3G handshake because it can see a valid tower.

[thriftwy]

It may happen with a lot of devices if 3G appears browned out to them and not just plain unavailable.