Active GPRS Repeaters?

Forgive my relative ignorance on the topic here; I'm just trying to
educate myself on my options. I'm looking for ways to reliably boost
signal on my GPRS phones from ATTWS (now Cingular) at my home. I live
in a 4-unit building in the middle of San Francisco, but both of my
AT&T phones drop calls and lose signal frequently, unless I walk to one
end of the house or another. Is there some sort of repeater or active
signal booster I can buy and install here to improve things? If so,
will it work with other GPRS phones or even DCMA? I've seen a few
models advertised (like the SignalReach SA300) but I'm not sure whether
these are worth buying.

I would appreciate any insight you can lend.

Thanks,

Joe