Push Effect uses an SMS trigger so it will send you an text for each message you get. The program allows you to filter your text messages so it knows what the trigger is, and then it basically erases the trigger message and causes Pocket Outlook to do a send/receive.

I'm not sure how Consilient works. It sends a text message when you sign up to determine that your device is valid. I think it sets up a proprietary exchange connection that uses the data connection. So whenever you get a new message in the inbox, Consilient's server pushes it to your device without using any text messages. I assume that battery life will suffer as with any other true push solution.