I email my T.. not often and only when something has happened that I want to be able to talk about in my next session or that I am coping with on my own and just want reassurance I guess.
He would take my phone calls if need be but for me.. i can email and express the situation fairly blandly. It puts the emotions out of my mind for a while.
The responses aren't indepth - just reminders that I can do anything that I set my mind to.. or that I am a good person and I am allowed to make my own choices (say emailing my ex.. )
I think that just knowing that the communication can be between sessions helps.. that I can lean on a professional helps me cope.