According to this accepted answer, there is no phone on the market today that is immune from "Juice Jacking"*. I think an easy way to mitigate this threat is to have a filter that blocks USB pins 2 & 3 and only connects 1 & 4. (see Wiki for pinouts)
I'm sure that I can't be the only one who thought of this, so I'll assume it's a hardware dongle of some type that I can use to filter power before it gets to my phone.
Is this a legitimate idea?
What hardware devices exist that allow this filtering?
Do any cellular phones incorporate this security feature in hardware? (akin a hardware switch that opens or closes pins 1&2)
*Definition: Juice Jacking is when a USB charger is modified so that it reads, modifies or deletes information on a user's cell phone. This can include stealing passwords or adding spyware onto the device.