Hi,
I have done this before, it works. lets see if i can remember the configuration steps:
Scenario, old ext. is 1000, new ext. is 3000.
1. In CCM, configure extension 1000 to forward all to voicemail.
2. In Unity, go to subscriber with extension 1000. Select greetings, configure the options to record using a particular phone extension. Record the greeting "this number is changed... new number is 3000".
3. Somewhere in the subscriber setting, there is this option, after greeting, select forward to subscriber after greeting. Select the subscriber 3000. Do not choose the option "take message after greeting"
4. In Unity, open the subscriber with extension 3000, Go to Call Transfer. Select "Yes, ring subscriber's extension"
Walah... If I'm not wrong, it should work. Call 1000, forward to voicemail. Plays greeting. After greeting, don't take message, forward to subscriber 3000, which calls the extension 3000 instead of going to greeting.
HTH,
Eugene