I've used Sprint 1xRTT for 2.5 years, anywhere you have Sprint coverage, you have the avg 50-70k. Sometimes this goes to 10-30k, but often it's 100k+. EVDO is coming for Sprint at far faster speeds, but in limited geographies. Verizon is way ahead with their EVDO roll-out.

Cingular has EDGE everywhere too, 100K+ avg. UMTS is in 6 cities now at 200-250K avg (384 top). GPRS is available for Cingular and T-Mobile, but that seems too slow for me and I've never bothered trying it.

It's a toss up though, Cingular will be consistent everywhere at 100K+ (and UMTS supports voice+data), Sprint/Verizon will be slower where they don't have EVDO. I don't know what I'll do personally, as I think I prefer 100K+ everywhere with EDGE versus 50-70K with EVDO at 200-2000K. Airports though should mostly be EVDO.