Which model of Uniden phone do you have? Do you remember the PIN that you have programmed into the phone? (If the PIN is not set, you can't access the answering system remotely. The Uniden phones that I know don't have a default PIN.)
For the DCT648, to access the messages remotely, dial your phone number and wait for the system to answer. Press 0 followed by your 2 digit PIN (within 2 seconds of pressing zero) while the greeting is playing. To play back all of the messages, press 0 2. If the unit is off, then you need to press 0 followed by your PIN (within 2 seconds) after 10 rings and the beep. Press 0 6 to turn on the unit.
Other Uniden phones use a 4 digit PIN. On the DECT1080, when the greeting plays, press * followed by the PIN. Then press 01 to play back the messages.
Uniden phone manuals are available at the product page (start at http://www.uniden.com
and search for your phone) or from the Support page ( http://www.uniden.com/scat/cordlessphones_mnl
) . On the support page, you will need to use the drop down menu to change the type of phone (if you have a DECT phone) and then search through the pages. The manuals are listed in numerical and alphabetical order. One manual will cover several phones if the phone supports multiple handsets. So ignore the number after the dash if you can't find your exact manual.
If you add a comment with your phone's model number, I'll be glad to check the specifics for accessing the answering system for you.
I hope this helps.