Yes, that's between wave providers: anyone can build a wave server and interoperate, much like anyone can run their own SMTP server. The wave protocol is open to contributions by the broader community with the goal to continue to improve how we share information, together. If you're interested in getting involved, here are a few things you should check out on www.waveprotocol.org:
- Draft Protocol Specification -- This is an early draft and will definitely change
- Community Principles -- Understand how this open source project works
- Architecture Whitepapers -- Learn more about the components of Google Wave
We're eager to hear your feedback, so please tell us about your interest, and drop a note on the technical engineering forum with your feedback.
Beyond the federation protocol, you may also be interested in learning more about the Google Wave APIs, as described on the new Google Wave Developers blog.