"I used this to devise a scheme for remote software upgrade over GPRS ..."

I, too, have a GPRS-based application that is capable of remote firmware upgrade. The device uses a SiLabs controller which, by virtue of its paged FLASH memory, makes IAP a piece of cake.

In my particular case the application program copies the new code into a DataFlash® memory and when it has been fully uploaded, a small piece of (separate) loader code erases the controller's FLASH and loads the new code.
Using GPRS guarantees a very high level of data integrity, because there are checksums on multiple protocol layers (PPP, IP and UDP). The chance of an error going undetected by all three of these checksums is astronomically small.