VOIP billing software using JSP/Java

Hi All, * I'm only looking for individual developer so please do not bid if you are a company * We have telephony system developed by inhouse team and looking for billing modules to be integrated to bill our [login to view URL] billing is done by carrier itself and we just use SIP trunk to do outbound calls and rest is taken care by carrier. Since carrier is doing billing and they don't allow small customers who are looking for fewer lines. This is our big problem because we are not able to support small customers. Most of our customers are telemarketers and they have campaigns to run on our Dialers using certain number of lines. We need to have a web based billing system so we can support these type of customers. Current software is designed & developed by us and I'm the lead. I have been looking some solutions like ASTPP & jbilling etc to fulfill our requirement. We are on windows platform and may move to Linux in future. Our current configuration related stuff is maintained by web interface using PHP & MySQL database. I would prefer to use JSP technologies as we have very less power under PHP environement. As for requirement goes, I think what I need is to have a nice interface and have two models to go with - PrePaid & PostPaid. In PrePaid model, we will have some depost in account and Dialer will check balance before making calls. For PostPaid model, We can have bill cycle selectable by admin ( let's say weekly , monthly etc) and I'm thinking to use flat call rate ( say 1 cent per minute) and we will have specific campaign ID to bill against and that will have all detailed CDRs. It seems the most simple model if you have previously worked on anything related to billing. I'm writing some CDR and it can be tweaked anytime based on requirements & design which we can discuss after project finalization. I'm looking for someone who has developed & integrated billing software in past and has extensive knowledge in Java/JSP technologies who can closely work with me. I would prefer to use some open source project like jbilling or ASTPP etc.. but if you have some other ideas you are most welcome. I can give more details once I get response from you and your skills,experience [login to view URL], please do not respond if you don't have experience in Java/JSP environment. thank you.