I'm thinking Desert Run.
Once over the border, (well technically but definately further into Namibia), you must have international roaming activated on your phone otherwise you won't be able to make/recieve calls.
Question: Does GPRS/Internet ability on the phone go hand-in-hand with international roaming? Layman's terms: If you don not have international roaming enabled on the trip, your GPRS will also not work?