Catch NPE thrown by APN provider.
Use APN defaults when no other APN information is available.

Provides an in-app source for APN info for use in the case that the
device store is unavailable and the user hasn't provided local
connection parameters.

Only covers T-Moble USA, AT&T, and Verizon right now. Only T-Mobile is
tested. Other carriers can be added and tested on an ongoing basis.