How do I retrieve the messages

We do not have this, you may be able to buy a download here.
User guide Instructions book Service manual

You can download the manual from the manufacturer's web site at
http://uniden.com/index/manuals_results.cfm?cat=1

The remote access instructions are in the fifth column of the first page of the manual at
http://www.home-electronics.net/USER-GUIDES/29888_DOM_EN_AN_IB.pdf

Follow the instructions beginning on page 62 of this manual.

Hello,

When you are away, you call your number and waiting for the welcome message (your message). When the machine invites you to leave a message you enter your secret code, the one you entered when you configured the machine. (Usually there is default, but since you don't have a manual there is no point guessing (although 123 may do the trick). Some older phones have a code sticker on the underside of phone.)

When the code is recognized the machine starts giving instructions press (number) to (do something).

Hope it helps.

It's either a message stored on the device itself, or you unknowingly have remote voicemail with your phone service provider.

Call your phone company or visit their website for instructions on how to retrieve remote voicemail.

http://www.retrevo.com/search/v2/jsp/mytrevo/myTrevo.jsp?page=man

This link will give you the entire manual which will include your answer.

you can contact your mobile provider customer service and have them better assist you

On my Uniden (not sure the model) I press 0 during the outgoing message and then my 4-digit pin