HI,
Glad you got your GPS working. I don't know type of phones you have available, but if they are Win6-7 phones, there is a program out there called WiFiRouter (costs, but it works great....use it all the time), then you can use a free program called WAZE that uses online data. I find the routes selected, but the the nice thing is that it is "user-interactive"....that is, users identify construction/police/slow-stopped traffic. It should work great in DC. Other than that, I'd go with CoPilot for now because it's cheap. Magellan and Garmin have operation apps for the iphone, but not the Android Market yet, and those are the 2 companies that I would recommend.
Personally, my current setup is a Garmin 4390 standalone, with WAZE running to let me know where the traffic and cops are. Haven't had the Prime long enough to see if there's any others available....The other company to look at is Tom-Tom.
If you're going to connect the Prime to the internet via the phone, then you probably need to apply this fix, so ad-hoc networks are available. ICS stock has them locked out.
If you have an Android phone, there are apps similar to the WiFiRouter, I'm sure.
Good luck,
Bob