EVDO technologies in general are very unorthodox. They go to disconnected state in 20 seconds and used a stacking and queuing technology that adds additional latency. You can do network speed tests and get impressive numbers, however there are latencies that are often not accounted for. When creating sophisticated applications that use these networks beware. You will see latency in your application(s) and the carriers will never tell you why when you delve into figuring out the mystery of poor performance. Most think these networks are for browsing and email which queues messages by default. Other things that occur is network switching. If a network is busy the priority is for VIOP, you may do a data connection and see that the EVDO connection is dropped down to CDMA (dial up speeds). Most people are really impressed by EVDO. However, these people are also easily impressed by first impression using it in one location with good signal. With signal degradation or an area that has a lot of usage the performance numbers dive fast!
The bottom line is that an extremely thorough evaluation should be performed before investing in using these technologies.