iOS
Apple iPhone and other iOS devices don’t support the format natively. There are several apps available in the iTunes Store that do support the format including FLAC Player and Capriccio.
Android
From Android 3.1 (Honeycomb) onwards the OS supports it natively.
Alternatively you can convert FLAC files to the format of your choice, including the recommended uncompressed WAV and AIFF formats, or MP3 and AAC formats.