If you're always getting weird calls from area codes you don't recognize, Alltel's new City ID could be just the thing you need. Available only on the LGAX275 for now (more phones later), the app will display the city and state assigned to any landline or mobile phone.
If you want this, you'll have to fork over another $US1.99 a month, which is quite small compared to the $US27.5 billion Alltel itself just sold itself to a private group for. But if you're not on Alltel, apparently some other phones like the Samsung Upstage also have this feature. And Treos have an optional download for it too.
Product Page [Alltel]
Image courtesy blinman