Another thing to try is to delete your phone number and contact details in his phone, restart his phone and reenter them, then have him call you (try this first).
Quick questions, did you change isp or actual phone number? In any case contact your isp and delete/refresh your details in their system. Although not directly relevant, I changed from call only plan to a full data plan with the same provider. I also changed the phone number to a new one. This meant that the transfer from one plan to another did not process properly, fixed by them deleting my connection details at their end and me restarting to refresh them. This worked.
Another thing to try is to delete your phone number and contact details in his phone, restart his phone and reenter them, then have him call you (try this first).
