Texture compression Skybox seams

Trying to figure this out… There are seams in my skybox along all the edges caused (I think) by the texture compression, as the problem seems only apparent when textures are set to compression within Unity (for iOS).

http://img683.imageshack.us/img683/4927/screenshot20110915at202.jpg

They’re all set to clamp.

Well, you've basically answered your own question here. At this point, I would be asking myself whether the obvious seams are worth the one or two hundered K that you save on space. In what way are you compressing the texture? Are you doing it using the texture importer, or are you compressing the images outside of unity? If you aren't using any screen effects that need alpha channels on the skybox, change the compression method to DXT1 instead of DXT5 to get rid of some unnecessary data.