8.10.2. Feature Description 
The Preview key is typically used on a keyset with multiple lines.
By depressing the Preview key, the keyset user can see display information
associated with certain lines on the keyset, without requiring the user
to answer the call or to take the line off of hold.This "previewing"
can be done while the user is active on a call or while the keyset is
idle, as follows:
- A keyset user can preview ringing (audible) lines, for those lines that are configured to ring.
- A keyset user can preview lines on Manual Hold.
- A keyset user can preview lines that he/she has placed on Exclusive Hold.
- A keyset user can preview the currently active keyset line, (s)he is using, to show the identity of the other user and, when a call is camped-on, to show the identity of the camped-on caller.
- A keyset user can preview ringing (audible) lines which are recalling, i.e., from hold, park, system hold, and transfer.
An attempt to preview any lines not meeting the above criteria will give
a timed "CURRENTLY NOT AVAILABLE" display.