I just switched to T-mobile in preparation for receiving my new N900 (and saving $60/month in the process...happy bonus). One thing that I've noticed is the marked decrease in signal strength indoors due to the lack of 850Mhz coverage. Still, even with 1-2 bars of signal on the N95's meter, the calls are clear and I've yet to have one drop yet. So, while on paper it looks worse, in practice it seems to actually be an improvement in performance. Perhaps that's due to the oversubscription of AT&T's network due to the iphone...plenty of RF signal strength but the network falls down due to the load. Hopefully the same will prove true with the 3G performance as well..but I'll have to wait until my new toy arrives to test it.