How do I turn the intercom off at an individual handset?

SOURCE: no intercom connection between handsets

Here is a link to the uniden manual link and an excerpt from the manual section which deals with your problem :
http://www.uniden.com/products/productdetail.cfm?product=TRU8885-2

The handset doesn't
communicate with other
handsets.
• De-register the handset (see "De-register the Handset" on page 32) and register the handset
(see "Register the Handset" on page 68).
• Make sure that you have registered all handsets.
An extra handset can't join
the conversation.
• Make sure there are not 2 handsets already using the 3-way conference feature.
The handset or the base can't
join the conversation
• Make sure that another handset or base is in privacy mode.

To register a TCX805 handset, simply place it in the main base.
While the handset is registering, H a n d s e t R e g i s t e r i n g will appear in the LCD.
When R e g i s t r a t i o n c o m p l e t e . is displayed, the handset has been registered to
the base. If R e g i s t r a t i o n f a i l e d . appears, please try these steps again.
To register a ELX500, TCX440, or TCX400 handset, follow the steps below:
1) Disconnect the AC adapter from the main base.
2) While pressing down flash/find hs, reconnect the AC adapter.
3) On the handset, press and hold # until you hear a beep.
While the handset is registering, H a n d s e t R e g i s t e r i n g will appear in the LCD. When
R e g i s t r a t i o n c o m p l e t e . is displayed, the handset has been registered to the base. If
R e g i s t r a t i o n f a i l e d . appears, please try these steps again.

SOURCE: how to use intercom between two handsets

For models with 2 or more
handsets included
Making an intercom call
1 Press {INTERCOM}
2 To page the base unit, press {0}.
To page another handset, enter its
extension number ({1} – {4}).
The destination unit beeps for up to 1
minute. Someone else can answer the other unit and talk to you.
3 To end the intercom call, press {OFF}.