How do I manually transfer a call to voicemail?

If you need to transfer an active call directly to someone's voicemail because you know the target person is not sitting at their desk, you can perform a special transfer as follows:

1. Press the transfer key on your phone (some phones call it txfr, some call it trnsfr)
2. Dial *86 + extension of the destination party
3. Press the transfer key again to complete the transfer

*86 is a special system extension.  You can find a list of these extensions within your Admin Panel by clicking the Extensions tab.  You can also find this list at Key Code Reference and System Extensions

You can also use HUD to transfer a call directly to someone's voicemail: How do I transfer a call to someone's voicemail?