Well, that may be part of the reason it
isn't on the iPhone. Apple has a reputation for abandoning dated technologies earlier than any other company. I recently did some... er.. 'work' on an old iMac G3 from 1999, and it came with a usb mouse and keyboard (even tho the mouse wasn't even optical) and there was no trace of a PS/2 port anywhere on the computer. Apple is famous (or infamous, depending on how you look at it) for doing this kind of thing.
Also, remember that SMS and email are actually exactly the same thing, your phone number has its own email address with your carrier, and emails sent to this address show up as a text on your phone. You can actually email people on their phone directly, and they will get a text from a number such as 0 (101) 100-001 or something similar with your name at the beginning of the message. I'm not sure exactly how MMS differs, but
AFAIK it's still based on email.