On the Exchange Team’s blog, an article has been posted about Exchange 2003 DirectPush. An interesting read for all those that need to implement it. They also explain why DirectPush only works over a cellular connection like GPRS and not Wi-Fi.

The thing is, a GPRS radio does not consume power when no data is being sent/received. That is not the case for a Wi-Fi connection. Having to keep the connection going for the heartbeats would drain the battery very rapidly.