There's two main GSM signal providers in the US, and the other one is T-Mobile. As you indicate, the problem is your phone's frequencies - it's 900, 1800, 1900 mHz., and the US uses 850 and 1900 mHz., so you have only half your necessary channels. The only place in the U.S. that I'm aware of that uses the 900 mHz. band your phone has, is Washington, D.C., because of all the foreign diplomats and their cell phones. Your profile indicates you live on the West Coast, so I might suppose that moving is not an option.
Cingular is currently the largest GSM network in the U.S., so I'd guess their GSM signal is as good as it gets. If you're sticking with GSM tech, your only real option is to switch to a phone with the 850/1900 mHz. frequencies.
Does anyone have this phone in the U.S. and get decent reception? If so, who is your carrier? I have Cingular and because of the triband issue I can only get coverage outdoors. Thinking of switching to another carrier but only if I have some assurance that the performance will be better. Thanks in advance for your advice!