Channel space on an existing cable-TV system. Works in some places where cable systems are set up with excess capacity, requires cable company cooperation, and will likely incur regular fees. Telephone company data lines. This is by far the most common option. It is available most places, and requires equipment, installation, and monthly fees.
Many standards are available, and technology is mature, stable, and well understood.
Explore all of these options in planning your network. Most networks today will rely on the local telephone company offerings, but deregulation in this industry means that many new offerings will be available. Your local telephone company is likely to be a good source of information for connection options available. It has standards-based services that will offer you different levels of connection speed and cost. The oldest and often slowest option is the phone system and a modem.