I was surprise how easy it is to block your cell phone number from caller ID. According to About.com, all you have to do is dial three characters: *67. "This code is the universal command to deactivate caller ID... On the receiving end, caller ID will usually display “private number” because it has been blocked." If you have doubts about whether this works, there's an easy way to test it. Just dial another cellphone, and you'll see that your own number is no longer provided by their caller ID. (Instead, the phone will display a generic catch-all identification, like "Private Number.")
There's a reason why it's so easy to block your cellphone number from caller ID: your wireless carrier is required to offer this to every customer! "The FCC’s Caller ID rules protect the privacy of the person calling," they explain in an online FAQ, "by requiring telephone companies to make available free, simple, and uniform per-line blocking and unblocking procedures." But it's important to remember that *67 is a "per-call" block. "You must redial *67 each time you place a new call," the FCC explains.
There's a couple of important things to remember if you're blocking your own cell phone number from caller ID. Some people set their cell phones to reject incoming phone calls if they're coming from a phone whose number has been blocked from caller ID. At that point, a bigger question becomes: how do I then reactivate my phone number, so it's displayed on individual calls when it's important. The FCC's FAQ explains that dialing *82 should "unblock" your phone number, so it's displayed to caller ID, but only for the next call. "You must re-dial *82 each time you place a call."
But remember, the Federal Communications Commission also has clear rules prohibiting the blocking of phone numbers in certain cases. On their web site, they warn that telemarketers "are required to transmit Caller ID information and may not block their numbers." (If you've been phoned by a telemarketer who blocked their number from caller ID, you can file a complaint by e-mailing the FCC at fccinfo@fcc.gov, or by calling 1-888-CALL-FCC (1-888-225-5322).
Just to put it all in perspective, remember that the caller ID information can also be faked. The FCC warns that it's "susceptible to fraud" through a technique called “caller ID spoofing”. So even when the phone number isn't blocked from caller ID - that doesn't mean you're actually seeing the correct information!