On the Technobabbler blog, there's a quick look at their creation of a (weather) radar loop they could view on their cell phone.

I used the great mobile site from the NWS, but it still didn't give me the effect I wanted. And hey, I'm already filling a database with weather observations and radar images! So I decided to see what it would take to make a custom radar loop that I could get to at any given moment. The Treo can display animated gif files, so that seemed like the most efficient solution. The question is, how do we create an animated gif using PHP?

To answer the question, he found this script ("GIF images into animated GIF with native PHP class") and used it to create a simple script to grab the GIF images and combine them into a single animated image suitable for viewing in any browser. He includes the script used to generate it as well as an example of the result and how it looks on the phone.