I have had this problem with both of my Droid phones. Moreover, the first Droid phone I had, which was the original Motorola Droid, was never attached to any charger other than the one it came with, and the longer I had it, the worse it got; adoption of a passcode to activate the touchscreen mitigated it somewhat, but not entirely. (The second phone is a refurb, and I am uncertain as to whether it is the original charger or no, so no useful evidence there.)
Within a week of getting the new phone (the old one quit on me), it started doing the same thing, making spontaneous calls both to contacts (not necessarily recent ones) as well as random assortments of numbers, at various times, usually when it is not attached to the charger. It does sit in pocket in my backpack, but I have a passcode (not picture) screenlock. I have a bluetooth earpiece that I sometimes carry with it, but I have not set any voice commands for it, so I would find it troubling that it spontanously set up voice activation and started interpreting random passage of air molecules (or contact with the carrying pouch) as voice commands.
It is my one complaint about an otherwise fantastic phone, but it is getting tiresome. Is it the charger? Is it the bluetooth? None of the above? More important, is there any news/info about a software fix?