I am experiencing the same problem that is discussed at http://forums.timewarnercable.com/t5/Equipment-Voicemail-Features/Strange-Caller-ID-Problem-with-Tmo... except my cell phone is a Tracfone not T-Mobile. Actually, I have two Tracfone cells -- one a Smartphone LG L41C, the other a flip phone LG 430G. My TWC landline home phone recognizes an incoming call from the LG L41C, and displays its ID properly. But an incoming call from the LG 430G displays "Unavailable - unknown number" even though the number is listed in my TWC landline's Directory. This is a new issue. That is, for a year or more, the display for an incoming call from the LG 430G was proper. Now, a few weeks ago, it is not. At VoiceZone settings, I have "Call Blocker Select" for one phone number (not the LG 430G) and Nomorobo (for which many thanks!). I will appreciate any ideas.
For this issue, you would want to contact the phone carrier that provides service to phone and ask them to update the directory. Chances are the number that is being used was associated with a different carrier previously and when that information is not recognized, it will display as "Unavailable".