How do I setup the modem for a specific distinctive ring?

The +VDR command controls the Distinctive Ring option: Command:

+VDR=<enable>,<report>

Function: Enable/Disable Distinctive Ring (Ring Cadence Reporting)

This report format is one line per silence period and one line per ring period. The length of the silence period is in the form DROF=<number in units of 0.1 seconds><CR><LF>and the length of the ring in the form DRON=<number in units of 0.1 seconds>. The<LR>character is optional. The modem may produce a ring event code after the DRON message if enabled by the<report>parameter. The<report>parameter should be set to a value larger than the expected off-times within a single patter so that the Ring event reports are issued only during the off-times between complex patterns.

<enable><report>Description

0 na The modem will not generate ring cadence reports. Other call progress event codes are reported as normal.
1 0 The modem only produces DROF and DRON messages. Other call progress event codes are reported as normal.
1 non-zero The modem only produces DROF and DRON messages. The RING result code is displayed after the falling edge of the ring pulse.

For detailed information got to: http://www.multitech.com/en_US/DOCUMENTS/Families/MultiModemZPX/manuals and download the +V Developer's Kit.