Check out this JB APP called Calltell it tells you who's calling and also will read SMS. Very cool. It's $1.99 an works as advertised. Only for 3GS and iPhone 4.
CallTell For iPhone 3Gs And iPhone 4: Know Who?s Calling You Before The Phone Rings | FSMdotCOM
CallTell For iPhone 3Gs And iPhone 4: Know Who?s Calling You Before The Phone Rings | FSMdotCOM