It took a while, but the code for making my Netduino generate random call signs is finally working. I kept getting randomly occuring argument out of bounds errors. With a bit of help, I finally realized the cause of my problem was in the 0-based array and me not counting the elements properly. Duh.
The code finally works, and now my Netduino will sit there and buzz out random "call signs" forever.
Now to work out how to implement some kind of mode selection for buzzing out Morse code.