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I just finished re-wiring my workplace's new office, and noticed that many of the phone jacks in the walls were wired to use the 3, 4 wires in the jack, instead of the middle two. The middle most 2 wires were not hooked up, while the next two out from the middle were.

What would the use of this be? Maybe a special Voip setup? It was really odd to see...

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closed as off topic by Sathya, ChrisF, BinaryMisfit Sep 25 '10 at 11:19

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Some proprietary KSU or PBX systems use 3 and 4, but it seems unusual that the inner pair is not also wired. Are you in the US or elsewhere? What kind of phone system is/was in use?

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In the USA. The previous tenants had several large rooms for call centers/support and they were all wired this way. I don't know what equipment they had at all though. – BLueSS Sep 24 '10 at 20:31

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