Interconnected VoIP: what does it mean?

According to a Federal Communiacations commission's
definition, interconnected Voip has four main attributes.

1. They "enable real-time, two-way voice communications"

2. They "require a broadband connection from the user's
location"

3. They "require Internet protocol-compatible customer
premises equipment"

4. They "permit users generally to receive call that
originate on the public switched telephone network (PSTN)
and to terminate calls to the public switched telephone
network."

Federal Communications
Commission