The majority of my AW sessions were held online, over IRC. Depending on the kind of channel you're on, this has the advantage of having built-in dicebots, so you can have rolls basically as a regular part of conversation.
<Damson> I stick my gun into his face and very politely ask him for the keys to the trunk.
<MC> Haha! Great, so that's going aggro. Roll it!
<Damson> 2d6+2
<=Roll=> <Results for Damson [2d6+2]: 10>
<MC> Alright, since you have him at gunpoint, he rustles in his pockets and hands you over the keys. Looks like he has a few choice words for you, but he swallows them with a gulp.
<Damson> I bet he does. Now, lets see if I'm right about this trunk...
It's a very natural, and since the basic roll mechanic is consistent and dirt-simple, you spend no time with rule clarifications.
So long as you have easy access to an automated dicebot of sorts (would be surprised if Skype didn't have some sort of widget equivalent), I can pretty much guarantee the game will go as smoothly as a face to face one.