Customize the A2Billing front-end design and content

I would like to change the design of A2Billing front-end. It should be very light weight and simple to look. The unnecessary content should be removed. The directory structure should be in a form of restful uri. Please note that there are many pages in A2Billing, before bidding install it in local computer and estimate the time/effort on your part. One important thing, it must work with the existing backend (asterisk,mysql db etc..)