Until the iPhone gets some antivirus software on it, you will not see MMS (picture messaging) as a part of it due to the fact that someone could send you a MMS with a virus and you do not have the ability to accept or decline it so it could do nasty things to your iPhone.
Every phone that can do MMS can send them to an email address versus a phone number so I would tell your friends and family to send to an email address you have on your iPhone. I am also going to list some email formats so that you can send pictures to other cell phones. Every cell phone has an email address attached to it even if you don't realize it.
Altell : <10 digit Number>@message.alltel.com
Amp'd Mobile : <10 digit Number>vtext.com
AT&T: <10 digit Number>@mms.att.net
Boost Mobile : <10 digit Number>@myboostmobile.com
Centennial Wireless: <10 digit Number>@myblue.com
Cingular (AT&T) : <10 digit Number>@mms.mycingular.com
Einstein PCS : <10 digit Number>einsteinmms.com
Nextel : <10 digit Number>@messagin.nextel.com
Sprint : <10 digit Number>@messaging.sprintpcs.com or <10 digit Number>@pm.sprint.com
T-Mobile : <10 digit Number>@tmomail.net
US Cellular : <10 digit Number>@mms.uscc.net
Verizon Wireless : <10 digit Number>vzwpix.com
Virgin Mobile : <10 digit Number>@vmobl.com