Currently Sparrow supports most of the texture formats I would expect, which is nice. However, it looks like it's lacking support for Intensity + Alpha textures (IA8 as they're referenced in PVRTexTool).
This format is good when you want to use greyscale images for one reason or another. You can, of course, use other formats to accomplish the same thing, but you're either wasting memory (using RGBA8) or losing precision (using RGBA4). I've tested that iPhone does support this as a format.
Cheers,
--Brian
