Can I run a LAN and telephones on the same LAN cable. ?

Depends. If you are using 100Base-T4 standards - that is you want to use cat 3, 4 or 5 cables ALL 4 PAIRS (8 wires) ARE REQUIRED. If you are using 100Base-TX (category 5 or 5e cables only) or 10Base-T the wires numbered 4 and 5 (one pair) and 7 and 8 (another pair) are not used in normal LAN operation but should still be connected since some equipment may use them for special purposes (we use them for power-over-ethernet in special applications). The spare pairs can be used for telephony - each pair will carry a single analog line so a cat 5/5e cable can carry 1 LAN (10 or 100 MB) and two telephone lines. However you are taking a RISK that in the future some genius may invent a fantastic application for one or more of these pairs and you may have to re-wire. Whether you consider this a high or low risk is a personal decision.

When wiring an analog telephone line on a LAN cable the following notes may help:

1. All the LAN cabling MUST be category 5, 5e or higher.
2. A normal analog phone uses 2 wires or one pair.
3. If you are installing the cable and there is no EXISTING telephone connection on this cable use either spare PAIR of wires blue/blue-white OR brown/brown-white for each analog line.
4. If the cable has an EXISTING telephone wiring connection find the other end of the cable and confirm that it is using either the blue/blue-white or brown/brown-white if so proceed as per 3 above, if NOT move the wiring to use either of these spare pairs (failure to do this will leave you with non-standard LAN wiring which will only lead to confusion in the future).