NeumZ said:
why would that make it easier to shop for phones?

Because there are a LOT more phones with GSM 1900 than there are with GSM 850. You can pick up any tri-band GSM 900/1800/1900 phone - even import ones from overseas - and use it with T-Mobile. Can't do that with Cingular (unless you never leave CA / NYC).

all it does is limit the coverage area.

Not necessarily. I believe T-Mobile's GSM network is actually bigger and has better coverage than AT&T or Cingular at the moment. That will probably change as Cingular and AT&T continue to expand their overlays, but for now...

It's true that a single GSM 850 tower can "reach" farther than a single GSM 1900 tower, but all networks are designed to take those factors into account, and it's only an issue in less-populated areas.

A well-designed GSM 1900 network will provide exactly equal coverage compared to a well-designed GSM 850 network. The 1900 network (like T-Mobile) will require a few extra towers in rural areas to do that. But then again, T-Mobile has a pretty big head start - they've had years to flesh out their GSM coverage and optimize their network.

Bottom line, don't buy the hype that GSM 850 = better coverage. There are technical differences between 850 and 1900 frequencies, but that is accounted for in the network design. Coverage differences are usually due to other factors.