Most billing companies will utilize their own software and EDI thereby assuming the costs, however some billing companies including myself, in order to stay diversified and competitive will offer to provide the services utilizing the practice's own software and EDI solution but the costs would not be absorbed by the billing company in that situation. Generally with most businesses the client should never be charged costs associated with "doing business" and focus only on charging time, and costs associated with that client. There is no out-of-pocket costs for utilizing an already existent software and EDI solution, unless it's technical support, and if the client "wishes" you to utilize their software they would be responsible for costs. This would be one of the many incentives for them to move to your system in the future.