Phone automatically dials last call?!

[luv2chill]

You have a sticky Talk button, sounds like to me. Notice if you press the talk button twice you will re-dial the last call? if your button is on the blink it could be registering button presses.

Since you say it's used I'd strongly suggest that possibility.

And at that point, barring replacement of the device you'd need to see if the app AEButtonPlus (google it) will allow you to remap the talk key to do nothing. Then you'll have to use the on-screen talk button.