Why not have her SMS your email address instead of your phone number? It'll count as a MMS from her account but you'll save on the incoming text charge.
Though Twitter is a good idea too, but it sounds like she either likes her texting interface from her G1 (I'm assuming it's her's, and you have the iPhone?) otherwise your original plan of her emailing you would have worked out better.
Though Twitter is a good idea too, but it sounds like she either likes her texting interface from her G1 (I'm assuming it's her's, and you have the iPhone?) otherwise your original plan of her emailing you would have worked out better.