I would suppose it would depend....in my case, all of my "outcalls" have been at my apartment. The provider comes into the lobby, is greeted by the doorman, the doorman calls me to get my approval to let her up, and she arrives at my door.

Why do you ask? Maybe knowing that will help in getting the answers you seek...

Also, it depends on how much anonymity you require! If you need to meet the lady before entrance into the room it is probably a good idea to meet in lobby or cafe. If you're certain of liking the person than you simply provide the room number to the person.