What are people using for class 5 switch with customer/billing management

I am going to use it for prepay wholesale sip trunking.

No RTP media handling required. Also needs to be redundant.

Right now I am testing a2billing. Just because it's been around for a long time with a fairly active community and is totally free.

I looked at some of the paid offerings, which are kind of expensive at several hundred to several thousand dollars a month. When you are just starting out at 0 they are kind of expensive. Also most can't really do redundancy.

I have it working no problem with A2billing using free MySQL clustering. I also know Asterisk quite well and didn't have much problem getting something that just works. Not sure how well it scales for SIP only simple bridge traffic but I'll cross that bridge when I come to it