It seems annoyingly counter intuitive that an advanced smart phone like the iPhone does not receive proper picture messages like its inferior peers. Instead you are given a link to an awkward website that requires an intricate password and message ID. This is because of its standard SMS support, which is different than the versatile MMS (Multi Media) format. This dramatically limits the abilities that most iPhone users have, which comes as a major obstacle for those who have enjoyed the effective iPhone camera. Luckily there is a backdoor way of sending multimedia messages utilizing some of the 3G benefits.
What many people do not realize is that no matter what phone number you are working with there is an email address of some sort involved with it. The address for any given phone number is the digits of that phone number @ a specified email list for that specific carrier. For example, T-Mobile is tmomail.net and Alltel is alltel.messaging.com. You can usually figure this out by contacting the specific carrying company.
If you then want to send a multimedia message to a person from your iPhone you then have to email it from your phone. Go ahead and go into the email account you have synced to your phone. Go ahead and set an email message with the photo attached. In the address bar put their number @ the address that is set for their carrier. When you send it their phone will receive it as a multimedia message, just as if it was sent from a phone that offered MMS messaging options.
Reversely, if you want to receive a multimedia message you can go ahead and have people send that message to your email account. Once it has been received as an email you can open it on your iPhone and save it to your picture folder just as you would with a picture you find on a random webpage. You can also deal with it by making the image as large as possible and then taking a screen shot of it.