IPv4 and IPv6 don't interoperate; they merely coexist, the same way protocols like Appletalk and Netware used to. You should lean on your ISP's to offer you native IPv6 support. Unfortunately, in 2013 most of your clients will still only have IPv4, so any services you make IPv6-only will be inaccessible to 99% of the global internet (Google's traffic is running 1% IPv6 currently). Try to make your outward facing services dual-stack, supporting both IPv4 and IPv6. By 2017 most clients should have IPv6.