Interesting. I always thought some of that was in the background. My crackberry on AT&T/cingular droped calls all the time transitioning to cells.
In reality its all about the number of cells and the power of the over lapped signals. Alas issues I never had with my motorola phone on the same service.
In the aviation industry I have always heard that GSM/GPRS was actually the SATCOM system implemented on the ground. Same carrier band archeticture, same single cell (satelite) for serice. etc etc.
Can't really prove it per se. but I bet someone in the industry knows.