They can work between two committed adults who both want it to work, have enough disposable income to visit each other regularly etc.
However, between two teenagers, over-seas or not, it's unlikely. Just because they could find other people - in real life or online - they will most likely not, or rarely, visit each other - which is obviously one of the key things.
Another thing is that the teenagers may lay about what they look like, what they do, who they are etc. As soon as you lie in an online relationship, it won't work out of MSN/Habbo whatever.
So, I suppose they can work, but you have to be committed, and be able to visit each other.
