Currently with standard Apple music app and also other apps the playback is set to 16/48.
If one uses a standard idevice dac/amp on the market with (flacplayer app etc) their iphone/touch 24/96 files will playback at 16/48.
If one uses say another app (say flacplayer) this can expand to 24/96 to 24/96 etc if using a CCK and an external dac amp.
Skyn will playback at native resolution, for example 24/96 will playback at 24/96.
Ipads are another discussion.