We have an OS 7400 and are wanting to set up MOBEX on it. I know we will need an OAS card.I have seen the MP20 listed as working with the OAS. Will the MP40 work with the OAS? If so, do I need to leave slot 4 open?

Hi Greg, You can use a MGI16 card still all depending on the software level your running on the processors, this would be cheaper than a OAS card.
You dont have to put the MGI16/OAS in slot 4, the system can run it in many different slots but would be fine there.
Have you purchsed a card yet as i can get you one?
Regards
Phil

MOBEX on OS7400 requires a OAS card and either 4.3 software to do this via ISDN trunks or 4.4x to do it via SIP trunks.

The OAS card can go in any slot of any cabinet of the OS7400, but its best to put it in the main cabinet.

OAS/MGI card is only required if running SIP trunks and you want to use MOBEX. ISDN trunks do not require a OAS/MGI card to use MOBEX.

OAS cards provide the DTMF receivers required for MOBEX Executive (regardless of line type).
The OP hasn't specified which mobex they are trying to use (I made an assumption they were looking to use executive).

The OS7030/OS7100 and OS7200S (and I assume the OS7070) all come with builtin MOBEX DTMF receivers, but the OS7200 MP20 (the OS7200 MCP card doesn't support mobex) and OS7400 don't.