If not how do they keep track of repeat clients?

You can rest assured that once you have contacted a provider, you are in her list (whether by email or cell phone).  The same applies to any agency you contact.  This is the reason for a pre-paid cell phone and anonymous email accounts, if you are concerned about your private information. But then again, if you set up an appointment with a provider, I suspect you will have to divulge some personal info to gain access to a session...and you should be comfortable knowing they have your real personal info for as long as she is in the biz.

Those that say they keep your number, and do.
Those that say they do not keep your number, and still do so.

It would be a rare provider/agency that doesn't keep your number and other personal info.

that is how they recognize us when we call.   It probably only pops up a Nick Name...  but how else would the lady know she did not have to screen you again?  
OK, so the lady has the number to a TracFone...

i would be shocked if there was one that did not. there is alot of info available for a phone number and the person attached to it.