Everybody knows that using cellphones indoors can be a mixed bag: you might get lots of signal strength outside (standing in the rain) but once you step inside (where it might be, say, warm and dry) ...

Yea but phones have to be configured for UMA. With a microcell, any ATT 3G phone can use it. I honestly believe T-Mobile should do the same. It would be easier, and any phone will be able to use it.