Don't ever dial a toll-free number (one beginning with 800, 888, 877, 866, or 855 -- to which will next be added 844) unless you know the person or business you are calling.  Even if you try to block or spoof your own caller ID, the toll-free numbers ALWAYS get your real telephone number through ANI (Automatic Number Identification), a service the phone company provides separately or in addition to Caller ID.

ANI is always provided to toll free numbers because the toll free number is charged for every call you make to them, and the price can vary depending upon where you are dialing from.  It's different and much more accurate than the Caller ID service you get, and it cannot be blocked.

Your own Caller ID service is actually a "hack" first designed by AT&T to send similar information down an analog telephone line between the first and second rings.  Its only advantage is that it is sent in real time along with the call.  With today's phone services, it is easy to hack and, by law, the phone company is supposed to allow anyone to be able to block it (prevent it from being sent).  The caller ID name (CNAM) service is even less accurate than caller ID service, because it is just the result of a query using the (possibly spoofed) caller ID number into a commercial database that is probably independent of your phone company.  These databases are of varying quality.  Also, the phone company controlling the assigned number may or may not register the associate caller ID name in any database, and even if they do, they may not report it to all of them.

But all toll free numbers get your ANI, regardless of any blocking or inadequacy of Caller ID or CNAM.  So they KNOW your number if you call them back.

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