The GLS radio has some "hidden" menus for viewing information about the radio, upgrading firmware, and options for administrative setup.  These are not user-oriented options, so if you're simply looking to tweak radio options, this probably isn't going to have what you're looking for.  However, you might play around with it and find something interesting.

[size=4]Accessing the Menu[/size]

1. Turn the car on (just acc power is enough)
2. Turn the radio ON, then turn it OFF.
3. Press and hold the "1" preset button then, w continuing to hold "1", press "4", then release both.
4. Very quickly press "1" four (4) times.  If you wait more than a second or two, it won't work and you'll have to start again.

You will be presented with a basic info screen. 

http://inlinethumb64.webshots.com/45887/2987918820103135615S200x200Q85.jpg

Note: If you follow this same procedure with the "1" and "6" buttons, you will get the I think if you do the same thing with the "1" and "6" buttons, you get an information-only screen (menus are not available).

Also note that at either basic info screen, you can press the Info button to see more detailed information.

http://inlinethumb29.webshots.com/48220/2565043130103135615S200x200Q85.jpg

The Sub-Menus

At this point, you use the preset number buttons to select a sub-menu as shown in the picture below.  Once you've selected a sub-menu, you use the Tune up (^) and down buttons to select options. For most options, pressing enter will change the value for the option selected, but on the region menu, "Enter" selects and saves the region currently displayed.

Note also that you can't really "navigate" the menus. Once you select 1, 2, 3, etc., you're stuck there until you change/enter an option or turn the radio on, then off again and start over. In other words, you can't "go back".

Also note that after you've displayed this, you will most often have to turn the radio on/off twice to get it back to the point where you can start over successfully.

1 - USB Firmware Update (Self Explanatory)

2 - CD Firmware Update (Self Explanatory)

3 - GUI, Firmware Memory Copy (?) and XM DM Mode (?) - Not sure what the GUI ON/OFF item is for.  EEP -> NOR and vice versa are most likely to copy firmware from either flash (NOR) to EEPROM (EEP) to the other in case one of them is corrupted.  Also not sure what XM DM Mode is.

4 - Radio Level Monitor - Perhaps turns off monitoring of speed for automatic volume?  Not sure why since this can be controlled in the user interface.

5 - RF & BT Test and BT Firmware Update - Tests and an option to update the Bluetooth firmware.

6 - Country and Model - You can from a number of geographic areas.  In mine, only the US, Canada and Guam were availabie.  In other markets, other countries are available.  For each country, there is an option with or without bluetooth and other things (going by memory).

http://inlinethumb32.webshots.com/25375/2391136010103135615S600x600Q85.jpg