I found out that when I call some ANI numbers from my cell, it doesn't give my correct number. This includes all those famous MCI numbers. But several other numbers get my ANI just fine, and read back the correct number.
The wrong number I get is "not in service" when I try to call it. The area code of the number is the same as the area where I currently live, which is different from my cell phone's area code.
This seems potentially useful for fun and profit, if I can make sure my target is a number that gets the wrong ANI.
Is this some normal thing I just don't know about, or is this some fluke by Verizon?