WOW: Push Email can be expensive!
Setup Direct Push on an exchange server and did some testing with my K-Jam. Works good when it works, but monitored the traffic, I found about 400K - 500K per day just on heart beats! That's 15 megs a month, can be pretty pricey if you're phone provider doesn't offer a good GPRS data inclusive package.
Something to keep in mind if you're thinking of using it.