Well, if you are in a marginal or low coverage area for your GPRS carrier like T-Mobile, I highly suggest that you not get one of the newer quad-band phones. In other words, if you only get 2 bars of signal on your 7730 in your office or home, don't upgrade to the 7100 or the 7290. They both have the same issues of needing higher signal strength than the 7730 in order to properly find the network.
By the way, I should mention that I'm totally not happy with either T-Mobile's or RIM's support on this issue. On T-Mobile's end, it's clearly a coverage issue and should be remedied by increasing tower signal strength or whatever. On RIM's end, it's clearly a matter of phone design since the 7730 and the 6230s work fine in this building or in other marginal coverage areas.
Anyhow, guess I have to do another BB replacement. These quad band Blackberries have been a total pain in the ass. They have the features that people want/need (more memory and Bluetooth) but don't work properly in the building. What sucks even more is that if/when RIM comes out with an updated 7730, I'm sure that it too will be quad band and have the same issues.
And no, moving is not an option. Besides, there's no guarantee that we won't have the same problem in a different location. It's not like our particular corner of Palo Alto is the only place in the country/world with this problem.
So if you want a Blackberry with the best reach possible, don't get a quad band model. You might have better experience with a Cingular model since they are on a different band, but the phones will still have the same higher signal requirement vs the 77xxs.