Can you switch the Montgomery GI Bill to Post 9/11 if you haven't used any of it?

I am not sure about this one. I don't think you can switch as the 9-11 one required no installment payment for active duty members while the Montgomery GI bill required an investment of $1200 (I think that was the right amount)

Here is a link that may help.
http://www.benefits.va.gov/gibill/montgomery_bill.asp