Is this phone on the same node as your phone? If not 6 will likely not be the extension to access it. Go to the extension in programming, go to forwarding paths, open up the path to voicemail and change Fwd Call type - IC Calls to yes. Dial the extension of the phone and let it ring. Does it go to voicemail? Make sure that forwarding path is setup to go to the correct applications voicemail extension. This can be determined by going to the applications of the node the voicemailbox is programmed on (Example voice processor>Devices>Mailboxes> It will list the nodes, note which node the mailbox is on. Then go to Devices>Applications>Same node> and search for "Voice Mail" In the "Type" Column. Is this different than 6?