I have a NAV based '07 TCH and my Treo 700p failed only for OUTGOING calls if there is an unanswered Treo alert.
I ran ChatterEmail for a while and it would answer the alerts for me
but I had other issues with Chatter and uninstalled it.
I have since upgraded (@Sprints expense) to a 755p and have not
tested it to see if the same quirk exists.