I do actual sessions face-to-face, but I've had a few phone calls with my T and my marriage counselor that lasted 30 minutes when I needed to talk or was upset about something, so it was practically a session (they don't charge for phone calls). I've found it different, but helpful, for the most part (see #2 below).

Two things:
1. It was easier for me to talk about certain things, like I could admit to my MC that I loved him, which would have been much harder face to face.
2. However, it's also much easier to have a misunderstanding over the phone, where you don't have eye contact or body language--only their voice and words. MC and I had a big misunderstanding on a phone call that led to a temporary rupture that probably would have been much less major if the conversation had been in person (we worked through it--everything's good now). So just be careful of possible misunderstandings.