Have them compose a message and in the subject of the message tell them type in myver and press space. If they type myver and press space, myver will be automatically replaced with their handheld model and OS version.
I had to do the same thing when we upgraded from 3.6 to 4.0....I just sent an email to all of our users and asked them to reply to it.
Make sure they press the space bar after they type that...or you'll get a bunch of emails with 'myver' in the subject line....
