1.  They are visiting and contact information is handled by a local agency.
2.  They have actually lived in an area, moved away and come back to visit... hence the area code matches.
Not necessarily a red flag - for well reviewed ladies you may even be able to tell by reading the reviews what city they were in at the time, and see changes.

A red flag, but in many cases not. I am a screeener/booker and several well-known traveling ladies will use my service just when in my area. Most will advertise my number so they can still answer their phone for calls from their home city.

The could be using VoIP (a.k.a. internet phone) service as their phone company.  Unlike regular phones, VoIP phones are not tied to the physical location, but to a special device that a VoIP phone company gives its customers.  When people move, they have the option of taking the device, along with the area code programmed into it, with them.

In a nutshell, the scenario could be something like this.  When the provider used to live in your area, she signed up with an internet phone company (like Vonage), and got the device.  Then she moved somewhere else, and took it with her, along with your local phone number.  Now she's visiting your area, and she brought the same device to use while she's staying there.