I believe that whomever his service provider is for the iPhone (mine is AT&T), he can just declare it "stolen," and they will disable it. It -- and your obligation for its "x" number of more months on your contract -- remain your responsibility, but the phone will be disabled from making anything other than a 911 call.
This would avoid the unnecessary embarrassment for your H to explain the situation fully to the cellphone provider, and would also allow the possibility that OW at some point would agree to mail it to him or drop it off at the apartment complex, as he asked. If not, you could eventually just ask what the contract buyout is and eat that $$$, along with the loss of the equipment itself.
