Their websites will either feature the same HTML markup which behaves differently based on browser size or if using SDL Mobile or similar technology, the websites might also present different markup or prioritize content differently based on the visitor's device.
It might be too early to tell, but I suspect the focus of the RESS side of mobile devices will be on images. For example SDL's Contextual Image Delivery will transform, deliver, and cache images upon request based on the visitor's context.