If you have only the base cabinet, you need to buy the TCIU as it fits on top of the TCOU dial tone board on the DK40i. You get four ports of Caller ID and these are assigned in programming to Lines one, two, three and four.

If you have an expansion cabinet, you can use one slot for an RCIU card. This also gives you four ports of caller ID but they could be assigned to any line you have, for instance line one, line two, line five and line six if you had two separate companies and wanted Caller ID on the first two lines for each company.

Also you can attach a RCIS daughterboard to the RCIU and have eight assignable ports of Caller ID. For instance lines one through four and nine through twelve.

If you had your DK40i equipped for twelve lines and wanted Caller ID on all of them, you would buy a TCIU for the base cabinet and a RCIU with a RSIS daughterboard for the expansion cabinet.

THE Bracha, old blond specialist in Rube Goldberg solutions.