Cell phone spoofing is the act of making it seem like a call is coming from a specific cell phone number or person when it is not.

Cell phone cloning is one way this can be accomplished. Another phone is flashed or programmed with your phones Electronic Serial Number (ESN) and Mobile Identification Number (MIN) for CDMA, or IMEI and SIM card for GSM, effectively making it a duplicate of your phone. This is one reason it is a bad idea to hand out your ESN or IMEI on the internet. Since the phone is a clone of yours, you will be billed for calls. This process is difficult to do, and isn't as common as it used to be, but it still can be done if the person cloning a phone knows what they're doing.

Phone number spoofing is more commonly used and only tricks a caller ID into thinking that a number is being called from. The perpetrator could call someone you know on their phone, but make it look like they called from your phone to the person being called. This method is usually done by means of a 3rd party provider that is in business changing phone numbers for caller IDs. Their service has legitimate uses, such as telemarketers that wish to display certain numbers on caller ids, private investigators and law enforcement.