While it's, among other things, big in Japan, IPv6 hasn't precisely taken over in the U.S. yet. But IPv6 has serious benefits for SIP, so we've made it a priority at Junction Networks to begin making our network and systems IPv6 ready.
Bar none, the biggest problem for SIP is NAT (hence the proliferation of SIP ALGs). NATs were invented to conserve IP space by allowing one public IP address to be distributed to many devices. Since in IPv6 there are literally billions of IP addresses in each network, conserving IP space is no longer a concern and NATs become unnecessary. Additionally, not using NATs allows the media stream between two phones to route directly to each other, instead of being proxied through a central party, which should improve network performance.
IPv6 will be a great improvement for the SIP world, so we're particularly excited about it. Currently, we are directly connected to the IPv6 Internet via multiple providers and have established network redundancy. Now that we have the network backbone in place, we will be implementing dual stack IPv6 support as we roll out new services and do system upgrades. It will be a while until we're fully IPv6 ready, but the project is in motion and gaining speed. Keep your eyes tuned to this blog for more information on our progress. To begin working with the IPv6 Internet yourself, you might want to check out Hurricane Electric's free IPv6 tunnel broker service.