When using a communications application with the modem, always go to the menu and select 'Disconnect' before leaving the application. If you leave the application without disconnecting, you can still go back to the application and disconnect.
If your Palm III is locked up or you have an error message that you can-not clear, reset your Palm III by gently inserting a bent paper clip into the reset hole on the back of your III. You will then see the Palm III screen say "Welcome to Palm III" and you can continue as normal.