If you are trying to get calls to forward to voicemail, do this:

1. Call the voicemail pilot and be sure it answers and plays audio.
2. Go to System\Station-Related Info\System Forward Paths\First Unprogrammed Path. Label this 'To VM' and program forwarding point 1 with the voicemail pilot number.
3. Go to System\Devices and Feature Codes\Stations\Whichever station you want to test with\Forwarding Paths. Right-click on the right pane gray area and select 'Add to Forwarding Paths List'. Click next. Select the forwarding path you programmed and click 'Add Items', then Finish. You should now see the forward path listed under your test station Forwading Paths list. Double-click on it and uncheck 'Station - Busy' and check 'Fwd Call Type - IC Calls'.
4. Under your test station, go to 'Flags'. Make sure the 'System Forwarding' flag is set to 'Yes'.

Giver 'er a try and let us know what happens.