no, it would work. it doesn't have to be DRM per se, just automated public key encryption and signing using something unique such as the phones IMEI number.

it is very possible to implement encryption and signing without having the user go through key generation etc. make it all transparent and give them a lock to click on if they want to make the message and attachments secure. PGP already has a similar product, and hushmail is pretty easy to use.