So one of the quirks of the MiVB, which in your case should work in your favor, is the system remembers the originally dialed DN and will send a call forwarded to that voice mailbox even if other numbers have been rung along the path. There's a couple of ways to work around that, but I won't discuss here because it's not relevant.
In your case, you would set your first alternative to be the ring group, and the 2nd alternative is voice mail. There's a few timers you need to be aware of: first is the Call Forward No Answer timer in the original extension's Class Of Service, that will control how long the phone rings until the 1st alternative reroute kicks in. The next timer to be aware of is the Call Rerouting Timer in System Options; this controls how long the call rings until the 2nd alternative reroute kicks in. The last timer that can impact your call flow is the Overflow timer on the ring group. That needs to be longer than the difference between the CFNA timer in COS, and the Call Rerouting Timer. So, for example:
- Extension 1234 needs to ring for 15 seconds, then ring Ring Group 5678 for another 15 seconds, then forward to 1234's voice mailbox. First you need to program your reroutes, so pick an available one (not #1, that's the default) in Call Rerouting First Alternatives and set all call types to "This" and your Directory Number to 5678.
- For Call Rerouting Second Alternatives, you may already have line #2 set up to go to voice mail (at least that's how I was taught to program these things, but it can vary). If there's not an existing line programmed to voice mail, set one up on an unused line (but not #1, that's the default and should be left alone).
- Now you can go into Call Rerouting and set your 1st Alternative and 2nd Alternative options to the lines you configured above
- The last step is to go into your ring group (using 5678 as our example here), and verify that the Overflow timer is longer than the difference between your CFNA and Call Reroute timer. So for our case if NACF is 15 seconds and Call Reroute Timer is 30 seconds, the Overflow timer on the ring group needs to be more than 15 seconds. It also would be a good idea to check Call Rerouting and ensure there's no reroutes programmed against the ring group DN there.