I just read in an article that came with my phone bill titled “Mandated Messages from the CPUC” the following:
When you call 900 numbers or toll-free numbers such as 800 and 888, the company you’re calling may be able to receive and display your phone number by using an FCC-regulated technology called Automatic Number Identification (ANI). With ANI, there’s no way to prevent your number from being identified during these calls. You canoot block your number from being displayed as you can when you call other phone numbers.
If you want to keep your phone number private, use a company’s regular toll number instead of the toll-free number. Or, call from a payphone. If you do use a toll-free number or a 900 number, you can ask that your number not be given to phone solicitors.
I had always heard that there was some technology that made it so your phone number could not be blocked. Now we both know its extent.