WHEN A CALL COMES IN THE RECORDER SAYS THAT IT HAS NOT BEEN SET UP. HOW DO YOU SET UP THE ANSWERING MACHINE?

If your Phone service is recording messages, that disconnects your line. You need to have them turn that feature off, OR set the answering machine to answer is less rings, say two or three. If the FAX machine listens to the line, it can still be set at a higher amount of rings, say four, and should still answer any FAX signal as it's sent to the answering machine.

Here is the manual for your phone. You can download the manual and the instructions for setting up your answering machine are on page 43:

http://www.uniden.com/pdf/DECT1580-3om.pdf

Setting Up the Answering System
You can set up your answering system's features from the handset. Only one handset at a time can access the answering system menus.

Note: If you have multiple bases, select the base with answering system you want to access (see page 15).

Recording a Personal Greeting
Your answering system comes with a pre-recorded outgoing message or greeting that plays when you receive a call: "Hello, no one is available to take your call. Please leave a message after the tone." You can record your own personal outgoing greeting. Your recorded greeting must be between two seconds and thirty seconds long.

Press /mute. The system announces the number of new and old messages, then starts to play the messages unless it has no messages.

Press 5 to stop the announcements or message playback. You will hear intermittent beeps indicating that the system is in the command waiting mode.

Press 8 to start the recording. The system announces, "Record greeting." Begin recording after the announcement.

When you finish recording, press 8 again or press 5. You will hear a confirmation tone, and your recorded greeting plays back for you.

Selecting a Greeting

Once you have recorded a personal greeting, the phone automatically switches to your personal greeting. You can
also switch back and forth between the pre-recorded greeting and your own greeting at any time.

Press /mute. The system announces the number of new and old messages, then starts to play the messages unless it has no messages.

Press 5 to stop the announcements or message playback. You will hear intermittent beeps indicating that the system is in the command waiting mode.

Press 6. The system plays the current greeting.

Since you neglected to specify the model of your Uniden DECT 6.0 system I can only suggest you select it from the list beginning here to download a copy of the manual.

Not sure if this will help with your query but it may be similar to the problem I had with a wireless home phone with answering machine not taking messages when I had the answering machine set to 12 rings before answering. Found the sim card (my wireless system) auto response would answer first. Fixed it by reducing time for the answering machine to come on to 6 rings and answering machine now comes on first.

Record Time sets the duration for recording the incoming messages. You have three
record time options. The options "1 minute" or "4 minutes" set the duration for
recording the incoming messages. "Announce only" answers the call but prevents
the caller from leaving a message.
1) Enter the Answ. Setup menu, and then the Record
Time submenu (see "Entering the Menu" on page 16).
2) Press volume up/down to select Record Time
(1 Minute, 4 Minutes, or Announce Only)
3) Press the OK soft key. You will hear a confirmation tone.

Well, your machine might be broken, or you haven't set the little switch on the unit to ANS. The switch is on the side of the machine where the cables come out. But here are the instructions from the manual:

Recording Outgoing Messages:

Your answering machine has a built-in outgoing message, "Hello, please leave a message after the tone." You can use this message or record your own.

1. Hold the ANNC/DAY/<<, and speak clearly into the microphone, no more than 10 inches away.

2. Release the ANNC/DAY/<< when you finish. Your answering machine beeps and automatically plays back your recorded message.

*Your outgoing message must be between one and 60 seconds.

*If you record your won message but wish to revert to the pre-recorded message, press DELETE during playback of your outgoing message.

GE Digital Messaging System ~ Voice/Time/Day stamp
1a] press and hold down STOP/set button and wait for promps.....
ie. press NEXT to change Day stamp and then SET to pick.
ie. press NEXT to change Hour and SET to pick.
ie. press NEXT to change Minute and SET to pick.
1b] press NEXT to pick 1minute allowance recording for recieving messages coming in, or 2 minutes or 3 minutes or 4 minutes. This machine only has 1/2 hour of recording time, so maybe you can 'tell' -record- that and let incoming callers know they have only minutes and machine will automatically shut off and cut them off [hang-up] on them.
2] press and hold down Greeting button and follow promps to change the answering machine voice promps to your own voice. Machine will automatically PLAY BACK your voice, if you don't like what you hear, press and hold down Greeting button again and try again.
~ hope all above helps.

I can't seem to get the security code entered.  It won't change.  None of the numbers will change when I try to set it up.

Try setting the receive mode to FAX/ANS. If you want the fax not to pickup before a phone call comes in, you should set the number of fax rings to a higher number, like "5" for instance. Set the answering machine rings less and the fax higher. The machine will usually record a message first and then detect a fax tone.

Make sure answer machine function is turned on. Bottom right button.
Make sure an outgoing message is set. Should see a <-> arrow in the display screen. If not, press the <-> button. To record outgoing message... the press the middle button; record out going message; press middle button. Wait a few seconds and you should be set. Hope this helps