We are teaching our kids to "plug in"!
And our parents complained about many similar trends when we were growing up (cough cough), and we turned out alright. Beyond that, my parents have confirmed

that it was the similar for them.
they are all plugged into something and communicating with ten different people at a time between cell phones, IM, and whatever else they have going on! I think it should cause concern!!
On the contrary, what you're outlining here is perhaps the saving grace. It reminds me of all the concern, 15 years ago, about children switching from board games to video games. What we ended up with was a much more technology-inclined workforce, which has greatly fostered our productivity and competitiveness in the world.
I'd worry about teens using hard drugs, not teens learning to multitask.
Kids nowadays are more social then ever, it's just that the medium has changed.
Precisely, and very well-put.
I'm sorry but I don't think anyone is all that important to have to be on the phone all the time.
Have many of them actually said to you that they're on the phone so much
because they feel they're "important"? I think it is essential to look at things at face-value, without projecting meaning onto those things that isn't there. As mentioned above, it is likely that they're on the phone so much because they're that social, and their social world is far more active and dynamic than we're used to.