This was posted by Mroberts but needs to be kept readilly available:
How to create virtual DN:
Well, you can go plug a phone into a jack and temporarily punch it down on the pair appropriate for the virtual extension i.e.. 300. Then assign the target line for that person's personal DID to the phone. Then do a line redirect (Feature 84), press the target line button, then press the IC button, then your destination code to get out (9), then the number you want to forward the calls to (cell phone or other outside number). You can then remove the phone and the cross-connects and proceed with the next number. Now, I haven't had good luck with hard call forwarding a phone to a mailbox and then removing the phone. It eventually says "not in service". The way I have gotten around that is to assign the target line to a hunt group (707) then make the first port of the voicemail (feature 985) the only member of the hunt group. Then create mailbox 707 and assign it to extension 707. So that the target line rings the group, which rings the voicemail. The voicemail sees the mailbox attached to the group and plays the personal greeting. But the only draw back would be that it is an either or situation. Either the person has their calls automatically forwarded outside the system OR they have the call go straight to their mailbox. Now if you choose the second scenario and have a NAM voicemail you could do an Outbound transfer from the mailbox. The person would record their personal greeting saying, "Hi this is Melissa, leave me a message after the tone or press 7 to be transferred to my cell phone."
Or, If you can dedicate a phone (an old one, beat to death works here too), hang it in the phone room and assign answer keys of your phantom DNs to this phone. The number of answer keys your system can assign is based on its software release and version. Then program the phantoms like real phones. Because the phones now have an appearance in the system they will work steadily. We haven't tested external call forward but have tested all other routing to Voice Mail. Or, THIS WILL WORK BUT THE INCOMING DIGITS MUST MATCH THE MAILBOX DIGITS, ANOTHER WORDS IF YOU HAVE 4 DIGITS INCOMING YOUR MAILBOX HAS TO BE 4 DIGITS. Line Programming: 1. Build a Target line, example: 145 2. Enter customer received digits, example: 4598 3. Prime Set: None Hunt Group Programming: 4. Select a Hunt Group number (1-30) 5. Accept the default Hunt Group Extension that is associated with the Hunt Group number or make a new one. 6. Add a Member DN to be that of the NAM Voicemail DN. 7. Under Line Assignment, assign the Target Line to the Hunt Group. 8. Shorten the Time Out Que to be the lowest, 15 seconds (default = 60) 9. Make the Overflow extension to be the NAM Voicemail DN. Mailbox Programming: 10. ADD a guest mailbox 11. Make the Extension of the mailbox to be the Hunt Group Extension