I need to run about 60 feet of thermostat wire. I have hundreds of feet of coated telephone wire. Can I use this instead of buying the real stuff? I experimented with a short 2 foot section at the furnace and closed the loop and the zone triggered so I know it works but are there any concerns out there?

If you have no funds, you could temporarily try a 60' piece of your wire to test. How many conductors does your thermostat need, how many conductors and what type of phone wire?
I wouldn't do it, have seen it done.
Your thermostat is 60 Foot away? Near you return air?

With a run that long the gauge of the wire will probably not be sufficient to carry the load. Telephone wire is of a much smaller size than standard thermostat wiring I believe.

That's why I was asking, if he needed 4 conductors and had cat 5, he could double up conductors.

I see your point. I was thinking of just the old standard telephone wire not cat 5 cable. The problem sets in with any large VA draw then the relays start to chatter etc.

Will it work, most probably. Should you do it? Absolutely not. Thermostat wires are color coded for a reason and wiring with the wrong wire will eventually cost you a transformer or a thermostat when you "think" you have the wires in the right place. 60 feet of wire is cheaper than a new thermostat or transformer, or worst case scenario a circuit board.