If developers write to UP.Notify, do they have to re-write the applications when the carriers upgrade to MAG 5+?
No. Applications written to UPNotify will work without modification when the carrier upgrades their Mobile Access Gateway. However, in order to take full advantage of WAP Push capabilities, developers would need to write to WAP Push using the Push Access Protocol (PAP). Refer to the “WAP Push, UPNotify, and SMS” document for differences between the three types of push messages.