What is the best way to discuss/plan/negotiate about code architecture remotely?

Question

Our team is distributed in space and time, so we have no ability to discuss the architecture of the code in real time. How can we discuss it via documentation: write code interfaces/ comment/ modify, track history of the code architecture? Are there some specific tools for this? What are the best way: class diagrams, code interfaces, something different? We are using c# and VS2010