Integration - (1) billing and (2) DNS - update?

I'm looking to implement a billing system with some amount of integration with Virtualmin. There's some enthusiastic comments in the forums here about AgileCo's AgileBill back in 2005, but that company's sites appear to be defunct. Is there anything newer worth looking at?

I'm also interested in integrated DNS registration. I'm an OpenSRS reseller, so I'm curious to know if there's any possibility of seeing that as a choice besides Register.com in the future?