I'd say that email would only work for an escort with an iphone or a blackberry.
While (PM personal message sent on EI) in essence is the same, I think those of us that use it - use it differently to how we would use email.
I would use PM to contact an escort that has stated in her profile that she uses PM. And I only use it to make an appointment in advance (ie. a few days). Otherwise the phone is the only way to make appointments on the same day - which I guess is what the majority of clients do.
"Don't be reckless with other people’s hearts. Don't put up with people who are reckless with yours"