Many providers will not take original phone calls from a cell phone, especially if you are a new client.

First call:  calling to schedule an appointment, usually given a cross street to meet at.
Second call:  confirming the appointment.  At that time she will give you directions to her location (if incall)

Roosta, I believe that you and I are the last two people on the planet not to own a cell phone, but here's what I do.

You may want to let her know your situation ahead of time if she relies on caller ID to help identify/confirm clients' calls. Always arrive at, or least near, her location very early to find a payphone. Usually, most hotels have a payphone in the lobby around restrooms or elevators tucked away in a corner where you can make a discreet call. (Although I have used the concierge desk with him standing right there easily overhearing.hehe) If you only have general directions, not specific location, such as "call me from the intersection of Walk and Don't Walk"; gas stations and fastfood joints usually have a payphone.

Take plenty of quarters in case you don't get thru on the first attempt. Many payphones will NOT dial out a long distance call, but will dial a  1-800 #. So I use one of those prepaid phone cards that is routed thru ATT's toll free number first, then you dial the number you wish to call from there.

If calling an agency, make sure they know to keep you on the line, or have you call back in 5 minutes while they check in with your date to see if she is ready for you.

It adds to the fun and adventure, I've got some great stories about this subject, ... but for another time.
best of luck, mr.man