Use of multilink interface

Hi,

I have one central Branch which I want to connect with 11 site branches,and in near future I have to implement 10 more.For this respect I have have taken 2mbps LL with Mux sharing 64 kb for each site branches.on the central site i am using 3640 router in which I am having 2 serial interface,now I want to implement the network where in near future if any new branch come I dont have to change any new hardware,In this regards I need help to implement the network and configuration?and will using multilink interface will be solution if yes can u give me some notes on multilink interface?