If you pick the right BYOD DIY ITSP (Internet Telephony Service Provider), the cost-to-benefit ratio as compared to the incumbent POTS (Plain Old Telephone Service) and Cable digital phone providers is off the charts. The incumbents just can't compete anymore (at least not on this turf).
One of the invaluable features I make substantial use of is called "Caller-ID Filtering". With two of my DIY VSPs (Voip Service Providers), this feature is free, as are most of their features.
So, how does Caller-ID Filtering work?
In simple terms, when an incoming call is being routed through my VSP's servers into my account, the server will assess the caller-id associated with the incoming call. If the caller-id matches the filter criteria, the call will then be directed, or re-routed according to how I have configured the caller-id filter(s). If the caller-id of the incoming call does not match a number as configured into the filter, then no action is taken and the call proceeds to its normal call destination.
The available options as to how to handle a call once there is a caller-id filter match will likely vary from VSP to VSP. But, with my primary VoIP providers, I have lots of options as to how I can handle calls through my caller-id filter. Oh, by the way, did I mention that these features are often free if you pick the right low-cost BYOD DIY ITSP's.
With my primary VSP's, one of the important caller-id filter options is to block calls that come in as "anonymous". This is a handy feature to use, for obvious reasons.
Other obvious uses of caller-id filtering is to block calls from telemarketers and other numbers that may be considered as annoying calls. Some telemarketers are very persistent and will change their caller-id each time they call. (This is known as Caller-ID Spoofing). Thus, it may sometimes be necessary to configure multiple filters just to block persistent callers using different caller-id's tagged to their calls.
Actually, just the other day, my cable provider's telemarketers circumvented one of my caller-id filters that I had set to block their annoying up-selling sales pitches. I had blocked their calls that were coming in as 855-835-xxxx. Next thing I know, they got me by changing their caller-id to appear as: 011-855-835-xxxx. Ok, now I've got a block on that number, too.
There are usually variations on how to handle an annoying caller-id. For example, I have the options to send to busy-signal, or send to a voice announcement message saying "this number has been disconnected", or "this number is no longer in service". These redirects will often discourage the most persistent callers after a while.
Other times, you may just want all calls from a particular number to be redirected to your account Voice Mail system. This way you can assess their messages and call them back another time, should you decide to.
There can also be other novel ways of handling filtered calls. For example, you may want calls from a particular number to forward to another number such as your cell phone, work phone, etc.
Caller-ID filtering is a great value-added feature (at no extra cost) provided by some of the VoIP providers that I like and prefer to use. In my book caller-d filtering is a "must have".