The DKT phone have to run off of a digital station port. They will not work off of a tip/ring port on an RSTU. If you attempt to plug one in there, it will most likely be fried the first time ring voltage comes down the line.
I did not read far enough, sorry. Yes, you could re-punch the extension onto the Digital station card easily enough and renumber the extension.

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Intertel Telephone Repair
Toshiba Telephone Repair

[This message has been edited by paul144 (edited February 22, 2005).]