In this day of cell phones and number portability, area codes don't mean what they used to.  There are a few ladies that I've seen where I live with out-of-town area codes.  Technically, when they return from whence they came, they are "travelling".  They may also be using a local person to screen for them; someone that knows the local market.

It may be a red flag, but only in-depth homework gives you a complete answer.

Do a TER search on the number and see if it comes up with any reviews. Sometimes visiting ladies book through a local agency even though it may not say so in the Eros add. Also, some ladies are not actually "visiting" they are local trying to attract interest....and of course some of it is bait and switch...

Not an obvious problem

As mentioned by little phil, area codes don't have the geographic meaning they once had.

The number that will ring a cell phone depends on the SIM card (the chip) currently in the phone, and it is easy to buy chips wherever you may be.

Also remember, we live in the VoIP (voice over internet protocol) age!  With services like Vonage and Skype, no number is truly local.  I live in England, but for only $30 a year, I have a Phoenix number that my Mom and friends can call me free.

You're showing good instincts,

jazz32

Couple of hints:
1) Google the number!  If 15 different providers show up, it is either an agency, scam or LE.
2) Definitely search TER.  I've cried when it came back with no results, but its safe.
3) If you are really paranoid, use one of the reverse phone number look-up services on the web.  You can subscribe for a year or pay as you go. (about $16/search). Unless the number is truly unlisted, you can get name and address and sometimes a lot more info.  Even if you don't pay, you can learn what cellular provider is being used, where the phone was originally "issued" and this gives you city.

I wouldn't worry too much about the "local" vs. other aspect.  The actual number means nothing.  More important to know about the provider!