You must install at least one TA S0 in the optiPoint master telephone. In this case, you can connect a maximum of two NI BRI data devices with S interface to the TA. As an exception to the "3-device rule" that applies to the SLMO card, you can also configure an analog device (for example, a telephone or fax device) on each of the NI BRI data devices with S interface. If you install a TA t/r (analog adapter) in addition to the TA S0 in the optiPoint master telephone, you can connect only one NI BRI data device with S interface to the TA.