Quote:
Originally Posted by Biggles
If it is a feature phone, it may have four wires. Typically on our mini-switches such as Panansonics the feature phone has extra functionality and works on four wires.
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This really only applies to commercial systems though. All the domestic speakerphones I've ever come across are 2 wire with even the ring connection being unused. The commercial systems use 4 wires to support things like putting callers on hold or transferring the call to a different extension.
Of course, if you find a phone in a skip then it may well have come out of an office and require a 4 wire connection.