I discovered that my phone company had numbers in the same area code that were "medium distance". You dialed them like a local call and they were in the same area code, but they would inflate your phone bill in a hurry. It wasn't easy to figure out if a number would be in that zone either. I had to cancel my first ISP after getting the monster phone bill at the end of the month. Luckily they weren't full up long distance or it would have bankrupted me, also lucky that I only joined the ISP in the middle of the month.