The closest you can do is to have the users CFA their phones to voicemail or other. Then within AC it will show the little call forward icon. Caveats are that the CFA icon won't show unless you are displaying something like 10 phones or less in the directory and it won't work in the speeddials either.
This was one of the reasons we switched to ARC at one customer. The CFA information works alot better and you can place notes on directory entries for precisely this reason...although it requires the operator or admin to add the notes to the directory.
Cheers,
Vance
