I tried some and it works, you can send MMS to most anyone by using these:
Alltel = xxxxxxxxxx@message.alltel.com
AT&T = xxxxxxxxxx@mms.att.net
Boost Mobile = xxxxxxxxxx@myboostmobile.com
Cingular (AT&T) = xxxxxxxxxx@mms.mycingular.com
Einstein PCS = xxxxxxxxxx@einsteinmms.com
Sprint= (xxx)xxx-xxxx@pm.sprint.com
T-Mobile = xxxxxxxxxx@tmomail.net
US Cellular = xxxxxxxxxx@mms.uscc.net
Verizon=(xxx)xxx-xxxx@vtext.com
Virgin Mobile = xxxxxxxxxx@vmobl.com
Links to the website's that i got this info from.1 and 2.
Alltel = xxxxxxxxxx@message.alltel.com
AT&T = xxxxxxxxxx@mms.att.net
Boost Mobile = xxxxxxxxxx@myboostmobile.com
Cingular (AT&T) = xxxxxxxxxx@mms.mycingular.com
Einstein PCS = xxxxxxxxxx@einsteinmms.com
Sprint= (xxx)xxx-xxxx@pm.sprint.com
T-Mobile = xxxxxxxxxx@tmomail.net
US Cellular = xxxxxxxxxx@mms.uscc.net
Verizon=(xxx)xxx-xxxx@vtext.com
Virgin Mobile = xxxxxxxxxx@vmobl.com
Links to the website's that i got this info from.1 and 2.