The RCIU2A will provide caller ID on 4 lines, gennerally lines 1 through 4 (although you could technically wire any lines for caller ID)
The RCIS1A is the Sub assembly for the RCIU, which will add caller ID to another 4 lines, for a total of 8 lines.
The RCOU3A supports 4 lines. It could have an RCOS3A sub assembly on it as well for a total of 8 lines. Each RJ-11 jack connects 2 lines, so if there are 4 jacks on the card, then you have an RCOU with an RCOS. The 'S" at the end of the part number means it is a sub assembly. The U menas if plugs directly into the backplane.
