I believe he is planning on using the AUTD feature of Exchange Server 2003. If this is the case those sms messages will cost you. You will need to figure out how many emails you get in a typical month and then figure out if it is cheaper to get a text plan or go w/ a per sms fee.

You may want to consider that if and when (refer to all the speculation posts) verizon releases the WM5 upgrade we will be able to get a true push email without SMS. In which case, you may not want to be locked into a text plan that you don't use.