It's probably through Caller ID spoofing. Callers hide their phone numbers by faking the information that appears on the recipient's caller ID. It can make a call appear to have come from any phone number the caller wishes.

To spoof a caller ID, caller can use the (1) typical spoofing service where customers pay in advance for a personal identification number, allowing them to make a call for a certain amount of time. The customers dial the number given to them by the company and enter their PIN. Then they enter the number they wish to call and the number they wish to appear as the Caller ID. Once the customer selects these options, the call is transferred and the person on the other end receives the customer's call. Assuming Caller ID is used on the receiving end, the receiver would normally assume the call was coming from a different phone number ? the spoofed number chosen by the caller ? thus tricking the receiver into thinking the call was coming from a different individual or organization than the caller's.

Or, (2) other Caller ID spoofing service providers also allow customers to initiate spoofed calls from a Web-based interface. Some providers allow entering the name to display along with the spoofed Caller ID number.

Either of the two, be aware that even if the caller faked the number on your caller ID, the real caller information is recorded within the telephone company's database. So if you want a specific call checked, you can have it pulled up based on the time and date you receive it.

---------- Post added at 11:41 AM ---------- Previous post was at 11:27 AM ----------

If you're considering spoofing caller IDs, I suggest you think again. Although you can hide your phone number, there are also apps used to reveal it. And if that happens to you, you might just get reported to http://www.callercenter.com and once you do, about 22, 000 people will be viewing your phone number everyday. With all those viewers, I'm sure some of them happen to like prank-calling, too. And you wouldn't like to make your home phone subject to prank calls.