The iPad will drop down to Edge if it feels the 3G signal isn't strong enough to pass data at the full rate.. Also, some carriers have Edge only cell towers.. My carrier (Roger's in Canada) did until last spring.. If you're between a 3G tower and an Edge tower, then the iPad could bounce back and forth between them. There's not much you can do about it.. My iPad would swtich between Edge and 3G quite often where I live until all the towers in my area were finally upgraded to 3G/4G.