Henk a.k.a. metaview once created a utility for PalmOS Garnet that I'd love to see on webOS:

The core feature (for me) was that it could notify you regarding the status of a call, e.g. via a few (three) short vibra buzzes.

You call someone, the phone buzzes when the other side picks up the call.
When the call is dropped or regularly ended, the phone will buzz again and (if set so) enter the sleep mode (so that it is locked and can be safely tucked away).

I hate the pre's behavior that I never "feel" if it has recognized that I wish to end a call. When I'm on the go, I want to put away my phone immediately after a call and be sure that it won't do anything in my bag just because it's unlocked.

So, in a nutshell:
Please make a patch that notifies you via a customizable signal or buzzes that a call has been established or ended. And add an option to immediately lock the phone after a call.

Original file by Henk can be found here:
Palm Software - pdassi.com PhoneDisconnect for Palm, Treo, Tungsten, TX, Zire: Alerts about missed SMSs, calls, and indicates the end of a conversation (signal)