You are correct, in 100BT you only use 2 pairs. My point was that using the extra 2 for phone service can provide mixed results. Try a POTS line on pins 4 and 5, with 90 VAC of ring voltage. Now, some US PBX's use digital on a single pair, and you may get away with that in most cases. Would I recommend it? Never. Wire is too cheap :-)

>Hi Jim
>
>As I said earlier, I may be wrong about the 1GB (I think I am right), but for 100MB I am 110% sure that you only need 2 pairs. It may be that the specs say you must use 4 pairs, but if so it is very strange that only pin 1,2,3 and 8 are used in all the equipments I have seen. In most hubs, switches and other peripheral equipment the spare pins are grounded, which is why you can not use standard patch cables if you want to share the cable with something else.
>
>It reminds me of the RS232-standard (well standard or standard, not a good word in this case....!) where you needed a 25-pin connectors with all pins connected in the beginning, then after a few years you only needed 9-pin connectors.
>
>>Hi Tore,
>>
>>The spec for 1000BT calls for all 4 pair - I thought you might have something else in use that got you around that. Off the shelf equipment needs 4 pair. I am surprised that you have no problems at 100 Mb splitting out pairs. Your luck is better than mine :-)
>>
>>>Hi again
>>>
>>>PLease forgive me if I am wrong, I have many computers and a mix of 100MB and 1GB. The 100MB I can positively confirm, about the 1GB I am not quite sure, but I belive it also only 2 pair? I must confess that where I have the mix of lan and PABX on the same cable, I only use 100MB. But at my office I have some offices where I needed more connections than I had prepared for, so I have splitted one connection into two, by using 2 pairs for connection one, and 2 pairs for the other connection.
>>>I am almost sure I also get 1GB connection speed in those cases, but I am not willing to bet, I may be wrong.
>>>
>>>>Really? How are you getting 1Gb speeds without all 4 pair?
>>>>
>>>>>By the way, I use it in a 1GB lan, so speed is not an issue here.