SDP and Backoffice systems

A net native ISV who builds a service and delivers it on-demand basically builds a new LOB. There are no legacy systems and the operations are confined to managing the infrastructure and adhering to the SLA's promised. However, for an existing ISV who has hundreds of existing customers, resellers who are managed by an existing suite of backoffice applications, creating and enabling this new LOB becomes a big problem.
Since the delivery mode of the existing software is following a specific route, integration for the reason of book keeping is absolutely necessary and most of the departments resist changes to th e existing process of order, invoice and payment.
Therefore the platform that is used to deliver the on-demand service would have to integrate with the existing back office systems, with data coming from back office systems to the platform or vice versa.
It will be interesting to know if there are any existing large ISV's who have gone through this process and if there are any interesting learnings that they have accumulated in the process.