Julius , i think i have the answer, the call would drop.. as the moment he crosses over to the other network area, the call has to be handed over from HPLMN BTS site to FPLMN BTS site.. which is not possible…hence the call would drop.The subscriber would have to do again a fresh location update so as to update the FPLMN VLR with its profile from the HPLMN HLR ,after which the call can be establish.