It's currently possible to fly/move through any "phased" objects.
I've only tested this on quest objects, but this is how to:
1. Have 2 Characters.
2. Acquire a double-seat mount.
3. Find an object you wish to go through.
4. Have the person(A) who the object is not showing up for, to use the mount.
5. Have the person(B) to sit on the mount.
6. Person (A) can now fly through the place where the object would've been.
7. Person(B) goes right through it.
Might be useful for something greater :P