I dial the TAPS DN and hit 1 for English, type the DN in twice as stated and get the following error message, "Extension is already in use".
TAPS doesn't like shared lines, so on the shared line, fill in a unique external phone mask, then type that in when it asks for the extension. (Or maybe it asked for the regular extension first, then the full 10-digit number which is the external phone mask.) I forgot.
This is because TAPS doesn't know what phone you intend to configure. Maybe they could improve it in the future to ask for the last 4 of the MAC address of the phone you are currently at or something.