Is this a question as to why it won't work or are you planning to get one and asking if it will? Your statement/question is a bit confusing.

I'm not sure what an 'XLink' is, but it if it is a device that provides industry-standard voltages, loop current, supervision and ringing protocols, then you should be just fine.

If my assumption is correct and this is just yet another VOIP gadget, then you'll also need to ensure that your line card is at least an 'E' version or higher or you might not get ringing. I'm assuming that you actually have a line card in the KSU for the third line.

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Ed Vaughn, MBSWWYPBX