This is asked often enough to be reposted indefinitely in the helpful links thread:

The "standard two call system" refers to the procedure often used when meeting with a lady at her incall, typically a hotel room. The first call is usually made the day of the appointment to first confirm the appointment and secondly get general location infomation, such as intersection of Walk and Don't Walk, or possibly the name and address of a hotel. Then the second call occurs when you arrive onsite at the appointed time. This is when you will learn her exact and precise location, room number if hotel or address apartment number.  

Although it may seem like you are jumping thruogh hoops or being given the run around, you must trust in the system. This "two call system" is mostly necessary and intended for safety and security of the provider. So be certain to follow her instruction for this procedure, maintaining an open line of commnuication, and to allow her to be comfortable when finally meeting you face to face.