The carrier question
After you've decided on 3G, the choice comes down mostly to coverage, performance, and pricing. You'll want to consider upload as well as download speeds. International roaming agreements are another factor to consider. If your users do a lot of international travel, GSM-based carriers enjoy a slight advantage.
Then there's the hardware. PC Cards vary in how well they hold onto weak signals, as well as the quality of connection software support for VPNs, authentication, and session management they provide. Some combine 3G with Wi-Fi and, on the GSM side, offer tri-band functionality for international use. If you're more interested in PDAs and smartphones than notebook access, consider the relevant hardware each carrier offers.
Carriers also provide some enterprise-level services, such as applications that offer session persistence as users move in and out of range, along with their 3G. Verizon Wireless offers its own branded business mobile e-mail solution, Wireless Sync, in addition to BlackBerry service, a field force management application, and a device management system that can remotely wipe data clean on a stolen device. Sprint is the only carrier we talked to that offered shared 3G services using a router. These can be used in the field or in a truck.
You can expect coverage to be roughly equivalent among the carriers by the end of 2007. The questions then become whether prices will fall or rise and how well will carriers handle increased capacity. For now, however, things look very promising. In our random testing with Sprint and Verizon Wireless, we found excellent performance that felt very similar to an airport Wi-Fi connection. And the freedom that 3G provides can be addictive. As with broadband and Wi-Fi, after you've tried 3G, it's hard to turn back.