A fun prank is to call friends, family, or strangers from the White
House's phone number (202 456-2121). The reason that this is possible is
that Vonage, Skype, and other VoIP providers fundamentally must be able
to fake caller ID in order to route calls from the internet onto public
phone networks (so presumably they've been doing some lobbying over the
years).
A Brief Technical Overview of Caller ID Spoofing:
What we'll do is register a free account at an ITSP, or Internet
Telephony Service Provider, which acts as the bridge between the
internet and the public American (or otherwise) analog telephony
networks. We'll then configure the ITSP to use the White House's phone
number as our outbound caller ID. Finally, we'll connect to the ITSP
using a free VoIP client, or softphone, to make our call using a PC.
The 10-Minute Step-by-Step Process: