When a person's cell phone/blackberry located in a pocket accidentally dials someone, unbeknowst to the person carrying it. The receipient of the call usually receives a very annoying, long and potentially incriminating message.
I swear I didn't call you at 2:30am last night-- my phone must have pocket-dialed your number.
In the cell phone age, pocket dialing is when your cell phone, seemingly of its own free will, dials your friends (or worse, enemies) at inappropriate times. This could be caused by small pockets or objects in the pockets that press buttons on your phone - including the send button.
I was totally making out with this chick when I realized I had pocket dialed my girlfriend. That was the last time she heard me moan - for some reason the bitch now wants nothing to do with me.
When your cell phone, whilst in your pocket, randomly calls a number.
Sam: (returning the pocket dial) "Hey Margie did you just call me? I answered my phone, but only heard you talking in the background."
Margie: "Oh, sorry man! I must have pocket dialed you!"