You can do that by going into Settings->Options->Screen/Keyboard-> Scroll down and you will find the Right and Left Convenience Key and there you can assigned what App or Action (Calendar) you want to assign . hope this helps.
I bought a Verizon Tour today and tried to change the convenience keys via the method described above, but instead of letting me change them, my phone just tells me how to do it, not letting me actually change the convenience keys.
Am I missing something blatantly obvious, is my phone just a dud, or did Verizon just decide that their Tour users don't need to be able to change convenience keys?
Any help would be much appreciated! This is annoying enough to me that I am contemplating returning to the Curve!
Thanks!