In order for you to insert symbols on a drop down list you have to inserted them by pressing alt-and the appropriate acsi number.
Unfortunadtly it seems like WORD doesn't like (&) the ampersand symbol which is AlT-38, but every other symbol worksso try ? ALT 21.
In other words after you enter AT Press ALT21 and add the last T and it will read AT?T. I know this is not the symbol, but I try ALT 38 and it doesn't work. As far as I know that's the only way you can add symbols on the drop down...
You can get the ANSI, UNICODE & HTML values at this website
http://www.hclrss.demon.co.uk/demos/ansi.html
Remember for ANSI Codes you press ALT first then the number...
Hope this helps...