Hi
Concurrent calls and negative balances are still an issue, because the customer's balance is updated at the end.
There are things you can do to alleviate negative balance:
1. Use the dial balance reservation parameter, this decrements the balance at the beginning of the call and puts it back at the end, so each subsequent call starts with less balance.
2. We have some diaplan for VoIP, that limits the number of allowed concurrent calls, see
http://www.asterisk2billing.org/add-ons ... ls-module/For some sponsorship, this could be modified to hangup all calls for that customer when the first call hangs up and the balance is 0.
Joe