Picture messaging is called MMS. The iPhone can send any photo you have via e-mail direct from the phone, so that kind of renders MMS obsolete. Of course, most non-iphones out there still don’t let you receive pictures in e-mail anyway, so that’s probably not a good solution if your trying to send a picture immediately to a buddy (who doesn’t have an iPhone).
Similar apps might include:
– the native app (if your phone is jailbroken) Twitxr, which sends a photo to your twitter account. Or the similar webapp Tittr
– there are many iphone photo sharing sites: Natuba, Smug Mug, and many more