Caller ID saves us time and aggravation by letting us know who is calling. Imagine going back 40 years ago, and not being able to see who was calling you. You would have no idea who was on the other end of a ringing phone. It could be your mom, a friend, a prankster, or a call center telemarketer. The only way to find out was by answering the call.
Nowadays, we still get annoying telemarketing calls, but thanks to caller ID we can ignore some of them, it helps us identify who is calling. With caller ID (CID), you'll be provided with the number that's calling you. Sometimes caller ID can also provide us with the name of the caller, this type of service is called CNAM.
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