with a bit of supervision yeah
If you are right there and you help them get it set up, and can see that's who he's really talking to - I don't see the harm.
Then it's not much different than a phone call really - why not?
The internet will only lead to hell.
If he's talking to a friend, no...it's not a problem! Just make sure that he is closely watched while on it!
I don't see why it'd be a bad idea.
only if their parents are present
If its a real life friend. At the age of 11 I started to play the game RuneScape. I made many friends over the game and didn't voice chat with them till I was about 14 or so. 11 is too young if you ask me.
If I was a parent I would want to sit in and chat with the friend too see what they are like. Good thing I am not a parent