My experience is similar to Mike's--it CAN be flaky, especially in metro areas where the towers are already crowded. That, plus it often seems that rebooting the router is the only fix for a dropped 3G network link.
If you DO decide to go with a 3G solution, at least make sure that you hardwire the three workstations to the router. Connecting to the router via Wi-Fi will compound your frustrations.
Is
this link of any use to you?