I received a package from Palm this morning. It contained a little plastic SIM card tray to replace the one in the top of my Treo 650. As per the accompanying note:
Palm has learned that some SIM cards may not fit tightly enough in the SIM tray provided with the Treo 650 product. As a result, the SIM card contacts may lose their connection resulting in possible dropped calls or occasional shutdown of the phone function.
My gut feel is that this cannot be the cause of the reliability problems that I (and many others) have experienced with the Treo 650. But, I’ve switched SIM trays, you never know.