I personally hate talking on the phone. When I talk to my T on the phone, on rare occasions,I'm all bubbly and chitchatty, nut thats mire to cover up my anxiety. I dont think I could do a session on the phone. Id miss to see her expressions because we work like that. She doesn't always say sth but I still kniw what she's saying. Od miss that nonverbal part a lot.
However, instead of not seeing her, I might agree to something like that in a special situation. Im not a skyper at all, so I really dont know about that... Itd help with the nonverbal stuff, but I'd probably be so freaked out by that video chat that I couldn't even look at my T.

I think it really depends on your personality. If you think it could at least be somewhat helpful, try it out.