There are two types of cables associated with Voice Over IP connectivity: Telephone wire and Ethernet cables. Telephone cable comes in two common varieties, the “line cord” and the “handset cord.” Ethernet cables are commonly called “Cat5” or “Cat6” cables, which causes some confusion. Cat6 cables are newer and better than Cat5, but, if the cables weren’t labeled, they’d look exactly the same.
Telephone handset cords are used on every corded phone, even IP phones. They are coiled and have special PVC shielding so that you can stretch and yank on them, and they’ll hold up. While they are most commonly six or twelve feet long, you can find cables for sale as long as 50 feet. If you have a PSTN phone, you plug a line jack into the jack in your wall or into your ATA. A telephone line cord is flat, and is typically grey, but sometimes black or white. The color has no effect on performance. They are analog cables designed to both move sound, and also conduct electricity, which is why PSTN phones work during a blackout. (Phone companies have their own backup generators). A line cord can carry different kinds of data, and is used in many applications, such as alarm systems, credit cards, and faxes. Inside the cord, there are usually four conductor lines, meaning that you can have two phone lines, each using a pair of conductor lines. There are specialty cables for different applications. HP, for example, recommends a cable with only two conductor lines for their fax machines.
Speaking of experts, while you may want to leave it to a trained professional, you can wire your whole house to VoIP using your home’s existing wiring. Using the network interface device, a box just outside your house, you can unplug and plug in the correct wires, then connect your VoIP device to the correct telephone jack in your wall. If you do it correctly, you can plug your legacy phones into phone jacks throughout your house, but get your service from a residential VoIP provider.
Ethernet cables are wider than telephone wires, and are often called “Cat5” cables, even if they are technically a “Cat5e” or “Cat6” cable. Ethernet cables are shielded against magnetic interference with a PVC jacket, meaning it’s covered in a special type of plastic. A Category 6 cable is designed to handle “gigabit speeds” of up to 2000 Mbps. A Category 5 cable can only handle “fast Ethernet speeds” of up to 100 Mbps. Generally, a Cat5 and Cat6 cable can fit into the same jacks, and Cat6 cables are backwards compatible. Also, just because it has higher bandwidth, a Cat6 cable does not necessarily mean you will see faster speeds – a chain is only as good as its weakest (or slowest) link. For VoIP, it is recommended that you have Cat6 capability. When you buy an IP phone, usually you’ll find a new Cat6 cable in the box. It’s one more way in which VoIP phones get you up and running in just minutes.
– Business VoIP Buyer’s Guide