In a 4e game a few years ago, we had a friend of the GM who was somewhere on the East Coast. He played via Ooma. It was mostly successful, but there were times when the connection was a PitA.
I think it went mostly well, especially considering the limits of the program at the time. I think Skype today is much more robust and versatile than Ooma back then.
For absent players, as a GM who dislikes killing characters without good reason, I usually NPC said player's character and limit their role in the session. They're not invulnerable, per se, but their limited role puts them at lesser risk.
Davy Jones
"Frightened? My dear, you are looking at a man who has laughed in the face of death, sneered at doom, and chuckled at catastrophe! I was petrified."
-- The Wizard of Oz