I have never contacted an AW girl unless her phone number is readily available. Occasionally I have used the 'public' e-mail but then I have a 'private' e-mail address
I'll only ever arrange a booking by phone, but I'm quite happy to email a girl on AW asking for her number. A fair few don't reply, but at least 50% of my AW punts have been with girls who didn't display their number and they were every bit as good as the ones who did.
If I were only prepared to occasionally ask for a number, I'd have missed a few good 'uns just to save a few seconds of effort writing an email.