ok, just found your Sprint settings in menu/options/advanced
(I am on Cingular)
I changed my "Message Service Number" to +17045020600
"Email Center Number" I left this at 6245 (could not find appropiate Cingular setting)
"MMS Gateway" to wireless.cingular.com
"MMS URL" to
http://mmsc.cingular.com
"Network Profile" to My ISP
Now I can add a picture to an SMS and it sends successfully.
Looks like Cingular MMS is working.