Didww
Sip with firewall/nat using asterisknetwork address translation (nat) is a common practice used in networks, and it doesn't play well with voip
http://www.didww.com/Knowledgebase/sip_with_firewall_nat_using_asterisk
App
Fonality offers voip gateway internet pbx office phone systems.
http://app.fonality.com/info/voip-gateway-internet-pbx.htm
Fonality
Fonality
http://fonality.com/trixbox/forums/trixbox-forums/trixbox-projects/howto-install-firestarter-firewall
Mail Archive
Mail Archive
http://www.mail-archive.com/asterisk-users@lists.digium.com/msg178977.html
Enterprisenetworkingplanet
With linux and wondershaper you can tune your network's voip traffic and improve the quality of your calls.
http://www.enterprisenetworkingplanet.com/netsysm/article.php/3608001/Asterisk-Give-VoIP-Traffic-the-Green-Light-Part-2.htm
Freephonet.com
Four years of experience with the best set of plans, services and devices for internet telephony.
http://www.freephonet.com/
Forums
Forums
http://forums.digium.com/viewtopic.php?p=33430&sid=71386fe2f8c0def5e5133e3cbbdd6151
Voipgate
Voip services, connect your voip server to our voip gateway and you can reach the whole world. we also provide a voip termination to the netherlands. see our tarif plan for our low prices
http://www.voipgate.nl/