Here's an interesting (and unusually high production value) video of an iPhone mobile interface for Moodle:
Moodle also has a Java-based cross-platform mobile client which is not as pretty but seems to have decent functionality. (My impression is that this is fairly similar to the state of affairs with Blackboard's mobile clients.) You can see screen shots here.
In the long run, we're going to need to think seriously about creating more teaching and learning affordances that are mobile-specific rather than just creating mobile interfaces to existing LMS capabilities, but this is still a good step down the road.