To transfer an active call to someone else's voice mailbox, while on the call choose the Transfer button on your phone and dial *95* + Extension Number. You may also see soft buttons on your screen for Blind and Attended; may also show B Transfer or A Transfer (for blind or attended respectrively) or simply Transfer. Choose Blind or B Transfer. You can also just hang up your handset after doing the transfer plus *95* plus extension number.
For Example: Transfer -> *95*100 -> Transfer
Your phone might also have a VM TRANS button on the home screen. If so, then while on the call choose the Transfer button, then the VM TRANS button, then either dial the extension to transfer to or choose the extension's BLF button on your phone if you have it. The VM TRANS button is really just a speed dial that prefixes the required *95* code. Choose Transfer again or simply hang up. The caller will then hear the voicemail greeting of where they were transfered to.