I have a Sprint T600 and a GSM T600 (using T-Mobile service, but device not purchased from T-Mobile) and must say that GSM Mail is the best mail app currently available. Although it does not support IMAP, it does have a lot of functions others lack. It checks for mail in the background - the display does not come on and you can use other programs while it is checking/receiving/sending. You can still receive or make calls while it is checking too. GPRS gives the ability for the checking/downloading to pause during a call, then resume when finished, thus no missed calls like you get with Sprint BC or any other mail program used on Sprint's CDMA network.

It also allows for an auto signature at the end of each email sent from the Treo, which surprisingingly Sprint BC does not (at least if it does, I have not found it). Seems that would be a requirement for Business clients.

The Best feature? It alerts you of new mail with a simple flashing * in the top left corner of the screen, rather than a full page notification that must be acknowledged to us anything else on the device - a real pain for anyone who receives a lot of emails throughout the day as you end up having to hit OK, GOTO, or SNOOZE everytime you want to use your Treo for anything other than email. Now it would be nice if this could be done for SMS messages as well.

If Snapper Mail had the functions listed above that it is currently missing (functioning in the background, simple new mail notification that allows use of other programs, etc) along with support for IMAP it will be the perfect ticket. But when?