Not sure if this is what you mean but I'll assume that those who don't return your call are those that you haven't seen before. Most state on their sites that 1st timers should contact them initially by Email or ask that you provide your birth certificate, a copy of your social security card that you got when you were 16, your mother's mother's maiden name, year and make of your vehicles, copies of your last tax return, your Supervisor's/Boss's home phone #, all your medical records for the past 5 years, six or seven references with phone #'s and email addresses and a stool sample. Its all very standard and quite routine.

TIREDOFBS seems to have gone off the deep end these days, I LOVE IT!  

Kyle made a good point... if you leave a voicemail requesting an appointment right now/within the next hour, if the escort didn't answer your call in the first place, most likely she is with a client and won't be getting back to you that quickly. She probably won't call you if it's too late to accommodate your last minute request.  

Another issue here is not leaving your phone number clearly enough.  My voicemail does not announce the callers no. and the callers number isn't in the 'Incoming Calls' list.  If the escort can't hear your number clearing she won't be able to call you back.
Suzanne

I always do my homework ahead of time and schedule in advance. Inital contact is made by E-mail. I always state in the E-mail that I would like to chat prior to meeting and ask what a good time to call would be. This seems to work out great. Also when leaving a message let them know if it is ok to call anytime or a no later than time. Of course it is just my .02 Hope it helps.