Blocking those nuisance phone calls that clog up your answering machine and make you get up from the dinner table has been of interest to anyone with a phone for quite some time. Now that it is becoming that much easier to originate such calls using Voice over IP technologies, the e-mail SPAM phenomenon is likely to play itself out in the telephony space as well. Thus SPIT will be the next frontier in the well-connected home's fight to maintain its boundaries.

As I see it, e-mail SPAM fighting techniques fall into two main camps:

• Know the Sender
  Under this appraoch the focus is not so much on the content as it is on identifying and classifying the senders of e-mail. Any e-mail from a source not deemed trustworthy is relegated to SPAM status.
• Tag the Content
  Using a variety of statistical methods these solutions inspect all incoming messages assigning each a SPAM likelihood percentage. Those that fall below the threshold are routed into a SPAM holding bucket, the rest get through.

However, callers can only be identified by way of their caller-id (CID) and unfortunately these caller-id values are easily enough spoofed:

• Orange Boxes
  These devices send call-waiting caller-id signals from the caller's side to the recipient once the call has been picked up. Thus it is not perfect but it can still be used to trick people.
• Insecure VoIP Providers
  There are some VoIP providers who will let the subscriber control the outbound caller-id number albeit not the name. This technique makes the calls indistinguishable from the real thing.

With the stage set and the "caveat emptor" in place, read on to see what individuals with VoIP service can do to cut down on unwanted and unsolicited telemarketing phone calls using the only weapon currently at hand: caller-id.