Hi
If you do not have DNS resolution on your system, then it's not going to work, your system will not know where to find it's trunks, because I'm guessing that you cannot ping anything, not just a2billing's SVN
VoIP telephony is about 80% networking and 20% telephony. If you cannot get the 80% correct, then the 20% is not going to work.
If this is intended to be a professional system, and you intend to have live customers, then you may consider getting some professional help from
www.star2billing.com so you can concentrate on the business of sales, rather than on the technology.
Joe