Customer Purchase History

Customer Purchase History

We are a company that sells online services.  I have customized the sales process from lead to close.  Once a sale is closed an account gets created in our online system. I want to list the active subscriptions in the accounts module. 

I am not using the 
sales orders or quotes modules.

Which module should i customize to display this information.  This should be identical to what Zoho uses internally. In other words, after the sales process I purchased the enterprise edition.  How is this displayed to the Zoho customer services reps when i call.

thanks
bruce