Per-call blocking will allow any caller in Maryland to prevent his telephone number from being displayed on a Caller ID screen.
Per-call blocking will work like this: Before dialing a number, you dial a two- or three-digit code. That's it.
Once the code, which hasn't yet been determined, is dialed C&P's network will not transmit your number to a Caller ID display device. So even if you dial a number connected to Caller ID, the letter "P" or "Private" will show up on the Caller ID screen, not your phone number. This will alert the person at the other end of the line that someone is calling who does not want his number displayed. That person can decide if he wants to pick up the phone, just as if the screen displayed an unfamiliar number.
That, according to the PSC, is the beauty of per-call blocking.
The downside, however, is that you have to dial the code every time you make a call to make absolutely sure your number is not transmitted to a Caller ID device. That's because you have no way of knowing -- unless someone tells you -- that the number you are dialing doesn't have Caller ID.