SMDI with an IVP8 isn't very easy. The first time I installed one I think it took like 30-45 minutes to get it working, with the help of a manual and another experienced tech. There is a lot that has to be done right for it to work. Generally providing programming instructions in the open forum are frowned upon by the board moderators, but here are all the things you need to have to get SMDI working on an IVP8

BSIS card
6 pin cable and DB9 modular adapter connected to the right BSIS and serial port
I/O devices configured for RS232 with the correct baud rate (default baud is usually correct)
SLT ports setup as Voicemail ports
Hunt Group with extension
VM ports setup as SMDI
Extensions set with center port and VMID codes

Voicemail setup with PBX type with SMDI
SMDI base port set (1st SLT port)

If any of the settings are incorrect and the voicemail doesn't know where to send the call, it goes to the default main greeting.

Also, BTW, I am sure if you look at your extensions you probably have 8 SLT ports set as Voicemail ports after initializing. The PBX just assumes that all 8 port work because it doesn't know how many ports are licensed on the IVP8.