When it comes to connecting multiple computers to a 3G connection on the road, you need a mobile router or a personal hotspot. There are several on the market, but most of them are self-contained and won't let you use an existing USB modem for connectivity.
A new mobile hotspot called the Wi-Reach has been unveiled at MWC 2010 by a company called Connect One. The device is battery powered and charges via USB. It has 5 hours of run time per charge and a built-in USB port for plugging in your modem.
The device supports 3G and 4G USB modems and can connect up to ten computers to the internet via WiFi. The router is available direct from Connect One for $99 and will be offered through private label programs as well.