The first was the problem, where attacker somehow got login and password (i think they broke thier ATA) from clinet and used it. But for this client there was a limit of one line. I used limit module with local database. What attacker actially did, is that they used REFER attack, where they put their own number as a referrer, and opened unlimited lines to PSTN. So the, solution was - to replace limit functunality to opensips.
The second - it is not actually the FS issue. It is because Freeswitch is not flexible enouph to work at the low level where Kamailio or opensips operates. E.g, we programmed opensips to lookup for UserAgent database, we add useragent for each client manually. And only using client's IP and user-agent we allow this user to call to PSTN. We watch for blacklists of IP adresses, subnets. If it comes from Gaza, Panama, China we block it. And a lot of other things. Most of them is not out-of-box in opensips, but it is not hard to implement. All this functionality is very important. We lost about $10k last time. This is very serious.