I don't know what the Apple people do about this sort of thing, but there must be one on here somewhere.
iPhones aren't much use here - you have to jailbreak one (and totally void the warranty etc) in order to be able to download apps that can block calls. It's really silly since I'm sure it's not just escorts who might want this sort of feature on their phone; every single bloody phone should have the option!
Can you tell I've got an (old) iPhone?

Well, not for work - currently using a dinky Android one, Samsung or Sony Ericsson or whatever, for work and that comes with a few options for call-blocking software. It's absolutely brilliant for when I do something dumb like answer a withheld number caller who turns out to be, obviously, a total freak and then when I hang up he (and his mates, if he's just a silly kid) try to call me 1,000 more times. The blocking software answers and hangs up their call simultaneously almost, if you get me, so they don't get to go to answerphone or anything. It also deletes texts (or stores them in a special "These texts are from idiots so do not read if you're already feeling annoyed today" folder).
To the OP (and any others wondering on this same topic) - as with all hardware/software/non-sex-work-related issues, it's best to just Google your question. "
Call blocker app [your phone make and model here]" or "
how do I block calls on my [your phone make and model here]" etc etc will find you approx. 10,000,000 pages of information from places like techy blogs or techy forums in which plebs (like me, cos I don't give a damn about learning how phones work, frankly!) ask these questions all the time and mega-geeks spend ages writing detailed answers. You can find a handy walkthrough for ANYTHING, including how to block calls on whatever phone you have.