this is a guy you'd know, otherwise you wouldn't have his phone number (and in any case, he wouldn't want to get your MMS if he doesn't know you). if it's an MMS worth sending, why not just call/message him and ask him for his email address? And once you've got it you don't need to ask him again (same as how you got his phone number in the first place)
(there's actually a practical problem here in the iPhone's lack of copy-paste, but that's another matter
Yes, but then if your phone has a well designed address book (like the iPhone) then all you need is one piece â" their name.
That's not what he means. If you know someone's number, but not their email (either on your phone, or at all), then even with the best address book ever (like the Motorola V980), it won't help you.