[Scottish] ISDN card for laptop

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Can anyone recommend one that works? 

I have found someone selling the
BIPAC (Billion) ISDN terminal adapter - PC Card
and a much cheaper USB device from the same manufacturer, but cannot determine whether either will work or not.

I want to try using a laptop as a substitute for the very expensive ISDN test handsets (Harriers) that some BT engineers have.

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