edit: I've solved this now I think. What I had done wrong was create the assets badly. I don't know the exact reasons, but taking the standard unity export asset bundle script and adding the BuildTarget.iPhone (I had originally left out a couple important parameters)
I've included some asset bundles in the "StreamingAssets" folder. They load fine in the editor, but, although I believe I have their path correct, they fail in iOS.
If I build the asset bundles with their target set to WebPlayer I get this error from the device:
The file can not be loaded because it was created for another build target that is not compatible with this platform.
Please make sure to build asset bundles using the build target platform that it is used by.
(Filename: /Applications/buildAgent/work/f724c1acfee760b6/Projects/../Runtime/Serialize/SerializedFile.cpp Line: 210)
The asset bundle 'file:///var/mobile/Applications/5AB67DD7-DDA0-44EA-8E6E-DBCDE54E18E2/prpg.app/Data/Raw/AssetBundles/LevelGeneratorCrypt1.unity3d' can't be loaded because it was not built with the right version or build target.
But when I build them with their bundles set to iPhone the device just says : Failed to load Asset Bundle. And it does not tell me why.
I'm going to try exporting Asset Bundles in different ways, see if I get lucky.
But does anyone know what am I missing? Is there a guide to getting Asset Bundles working in iOS? (I'm pretty certain I've got the dataPath correct)