I have actually a similar setup that we use at work but we have the MB8000 router such as this one:
RfWeL - Rf Wireless Electronics :: Wireless Networking :: Mobile 3G Routers :: TopGlobal MB8000 MobileBridge Cellular to Wifi Mobile Gateway Router which supports both EVDO (Sprint, Alltel, Verizon) as well as HSDPA/UMTS (Cingular) as well as EDGE (T-Mobile). Work for an engineering company and we go out and do field training so depending on what geographic area we are travelling to we are able to determine before hand what cellular data network will provide the highest speed and then carry the appropriate aircard.
By the way if you are going to get these routers from anywhere I suggeset either
RfWeL - Rf Wireless Electronics - Welcome or
www.evdo-info.com as these guys know a lot about these routers and can assist you in configuration or setup. The carriers will almost always never help with this. Personally like rfwel.com since they specialize in other wireless electronics as well and have a very knowledgeable support team.