You might want to see if you can get an NEC certified tech to look at this.

There are different VM you can have on the 8100.

Something doesn't sound right. What is 717? IS it an extension or a dept group number? You should be dialing the dept group number AND it needs to be programmed properly in the inmail settings. I mean you should be able to press the VMsg button on the display. If THAT isn't on the display you are not programmed correctly.