Saw this on a wiki page thought it may be of interest:
The number 123-456-7890 is used for VOIP calls originating a PC.
This number is a generic caller ID number used by the SKYPE and possibly other VOIP (Voice Over IP) phone providers. Currently most calls made through Skype on a PC will show up on caller ID as 123-456-7890.
A call from this number may be from any of the 275 million subcribers of SKYPE, who may be anywhere in the world. It may a legitimate call from a friend of yours.
Recently, however, there has been an increased number of scam callers hiding behind this generic number. If you believe that Skype should assign a unique ID for all callers so that scam callers would be unable to hide behind a generic number, you may wish to contact them to ask them to make this change.
You can make a suggestion or a complaint here:
http://support.skype.com/?_a=tickets&_m=submit You can also contact them at their physical address:
Skype 22/24 Boulevard Royal
L-2449 Luxembourg,
Luxembourg (Europe)
Phone: +352-26-20-15-82
Fax: +352-26-27-05-88