I think Hedge tree is onto the most appropriate explanation. 

I think its just a possibility of the hyper-sensitivity of trying to be paying attention in case you receive a call or message, that in turn, makes a person sense the phantom alerts.

I've experienced the same things that have been described here, but...

My phone has never, ever had a "ghost ring" or vibration when it's not in my pocket, like laying on a table (have you ever had one vibrate on a table -- impossible to miss).   And the small "ding" announcing a text message never occurrs in error in a quiet place, only in noisy areas.