03-22-2010 01:35:00 PM
Are you having these problems only sending to people on a certain carrier? If it's not a network related issue then try a master reset the instructions are here
I am an AT&T employee and the postings on this site are my own and don’t necessarily represent AT&T’s positions, strategies or opinions.
11-22-2010 02:40:59 AM
if a master reset did not work see if you can test your SIM card in another phone to see if the same thing happens.
-if if does: replace the SIM
-if it doesn't: try for a warranty or insurance replacement