The caller ID service lets you identify any given phone number calling you. Incoming calls originating from people whose caller ID number is hidden show up as "Restricted," "Blocked" or "Private Number" on your cellphone's display. If you want to find out the real number behind a call that says "Private Number," there is a service available called TrapCall, which unmasks private caller IDs and lets you view the caller's real phone number.
Browse to TrapCall.com
Click the "Sign Up" button in the upper right corner of the TrapCall page.
Select one of the three plans offered. TrapCall's monthly plans are the "Mouse Trap" for £6.40 a month, "Bear Trap" for £16.20 a month, and the "Bug Trap" for £3.20 a month (as of June 2011). If you're only looking to unmask private caller ID numbers, the "Bug Trap" is a good plan to choose.
Complete the "Information About Your Phone" section. You will be prompted to enter your phone number, your carrier, and you will have to create a 4-digit pin. Be aware that as of June 2011, TrapCall only works with AT&T, Sprint, T-Mobile and Verizon Wireless.
Complete the "Your Information" section. You need to enter your full name, e-mail address and time zone.
Type your billing information and select the billing structure you prefer. You can select to be charged every six or 12 months, or on a monthly basis. Click the "Create My Account" button at the bottom of the page to complete the registration process.
Ignore or reject the next private ID phone call you receive. When you don't answer the phone, the call is sent to TrapCall. There, the real phone number is unmasked and then the call is sent back to ring on your phone, displaying the real phone number, not the "Private Number" ID.
If the person calling under a private ID is threatening or harassing you, keep a log of the time and date when you receive the calls and report it to your local law enforcement authorities. You can also hire a private investigator who provides this type of service. Call your cellphone provider and ask if it offers a service that discloses the number of private ID calls. Generally, phone providers will not disclose this information; however, if it pertains to a legal matter, the cellphone company may release the records. Phone calls that display "Unknown" as their ID are not unmasked by TrapCall. When the caller ID says "Unknown" it usually means that it is an international call.