TreoFlex looks useful, plus it has just been updated to work fully with the Centro

TreoFlex looks useful, plus it has just been updated to work fully with the Centro. "TreoFlex sends out a simple text message for ignored (receiver terminates without accepting the call) or missed (caller terminates or the ringing times out) voice calls. TreoFlex will work with both GSM and CDMA Treos. You can also send customized messages by entering them in the contacts notes of a particular contact. TreoFlex implements a sub-set of the functionality of TreoProc. TreoProc has additional security features and meant exclusively for Treo 600 and Treo 650 GSM smartphones. In case you already use TreoProc, you don't need TreoFlex." Looks actually a very good program plus it's free too.
[moblogging from my iPhone]