RJ11/R45 Wiring

I'm not sure if anyone can help since this is more geared towards networking but I'll give it a shot.

I've installed wall jacks and dropped cable for RJ45 connections but I've never really needed to mess with phone cabling. We've acquired a new office and the phone system isn't under anyones control so I have to drop some cable for new phone jacks. My simple question that someone hopefully knows....

Some of the RJ11 jacks in my main office that I've inspected are wired with 3 pair and some are wired with 2 pair. Can anyone tell me what the difference is? Both work fine. All phones here are setup with 2 lines. I'm guessing that each pair terminated onto the RJ11 is for 1 phone line? I say this because the fax machine jacks are only wired for 1 pair on the RJ11 jacks. When I drop the cable I only want to terminate what is needed onto the jack. If I only need to wire them with 2 pair and leave 2 pair alone for later expansion, then I'd rather do that.

Thanks for any responses. The only resources I've been able to find on RJ11 wiring have been for home wiring and not small office.

Hello again
A standard analogue phone just needs one pair, i.e. two wires, to work. The third wire will be one of two things. In older installations there used to be an additional ringing line to ring the ringer though this isn't used much now. Or, more likely, the third wire is for use with a PBX to signal to the PBX that you want to sieze/release the line
If your phones are all working with just the two wires (single pair) then don't worry about the third one

Thanks for your response.

Now lets say I want to wire up a reception phone line that allows for 4 lines. Does that require any different jack termination other than 2 pair? Or is that all controlled on the opposite end on the punch block to allow for 4 lines?

I got lost there a little; do you mean you want to wire four phones in your reception over a single cable, or that you want to wire a single phone using a cable with four pairs?

Sorry for the confusion. By 4 line I mean the ability for the reception phone to receive or dial out 4 seperate lines at once. Our normal phones have the ability to receive 2 phone calls at once. Such as have one person on hold and dial out on the second line. I'd like our reception phone to have this ability with 4 lines. Does that make more sense?

Is this something that has to be done on the jack side or how its punched down in my telecom room?

I'd have thought the ability to handle multiple trunks was a feature of your site's PBX rather than the way the individual phones are cabled. Your other phones can handle two lines but they only have a single 'line' connected to them. Do you have a PBX on site? If so I think you should ask whoever looks after it if what you need can be done. If not, we'll have to think some more...