There are a number of Uniden DECT 6.0 phones. The user's manuals are available from the list here: http://www.uniden.com/index/manuals_results.cfm?cat=59
. Select your model and language for the appropriate PDF.
For the Uniden phone I know, you can set up the answering machine from a handset or the base unit. First turn on the answering system. On the base, press Ans On/Off. From the handset, press either the Phonebook or Redial buttons and use the menu to choose AM Operation. Then select Menu/OK. (Then find Answer On/Off choose On or Off and press Menu/OK to save.)
To set the Outgoing Message, use the handset as above but select Record OGM. (Alternatively, you can delete or hear your outgoing message.) To record the message press Menu/OK and wait for the beep before starting your message.
Next you can set the length of the message recording for incoming calls (1-4 minutes or Announce Only (no messages recorded). Choose Msg. Length from the menus.
I hope this helps.