I copied this from this forum.
Verizon-- @vtext.com
Cingular-- @mobile.mycingular.com or @mms.mycingular.com for MMS
T-Mobile-- @tmomail.net
Nextel-- @messaging.nextel.com
Sprint-- @messaging.sprintpcs.com (not positive on this one)
ATT-- @mobile.att.net
Alltel-- @message.alltel.com
U.S. Cellular-- @email.uscc.net
Bell Mobility-- @txt.bellmobility.com
Telus-- @msg.telus.com
Rogers-- @pcs.rogers.com