Emails: permanent written record I can refer to later
Can reply in my own time
Low labour
Low resource use
Phone call: Times/dates mentioned will be forgotten often
Active demand of time
I don't pick up because that phone number looks weird but also my phone's vibrate function is weak
High labour
High data cost per information
My shrink's office seems to want to keep billing information and past/present appointments secret. (This also seems to be worse in local industry, everything has to be a meeting instead of a two line email)
I have been nudged on the issue. You'd use text/phone as a walkie talkie and be responsible for emails the same way you might look at a pile of mail when convenient. That sounds cozy