The A2Billing project is not simply a billing interface for Asterisk: it is, in fact, a complete VoIP carrier-in-a-box. This complex and comprehensive product delivers much of the technology you would need to allow you to provide a VoIP reseller service.[176]
The A2Billing platform has been generously released under the AGPL as open source. The sponsor of the A2Billing project, Star2Billing, offers consultancy services to get you up to speed faster.
[176] It cannot provide you with business savvy, experience in running a phone company, or automatic security, though, so please don’t think that all you have to do is download A2Billing and you can take on AT&T!