HPNA telephone networks
If you have a telephone connection point in every room, you can create an HPNA 3.0 network.
HPNA stands for Home Phone Network Alliance, and makes use of your home’s telephone connection points to connect the network computers. Like Ethernet, it uses either a USB or a PCI or PCI-E NIC. You can create an HPNA network of two computers for under £60/$100 if you install internal PCI/PCI-E cards. A USB setup, which does not require opening the computers’ cases, just USB cables, is another option. HPNA 3.0 operates at 128 Mbps.
How Stuff Works – Phone Line Networking: