These earbud headphones are the perfect accessory for your FONA - they've been tested to work with Adafruit's modules - but can be used with any iOS or Android device that uses a TRRS pinout. The buds themselves are 16mm in diameter with a nice 40" long. They come with a standard 4-pole TRRS headphone jack and have a small microphone for phone calls.
Adafruit may change the model up but for now they are HTC 'OEM' brand in black. These particular headphones also come with a few add-ons which are a nice bonus. There are pads for the ear buds to keep your inner ear nice and cushy and a cool fish-shaped rubber thing for wrapping the cable around (the cable is a nice leisurely length)
Headphone Diameter: 16mm / .63"
Cable Length: 101.6 cm / 40"
3.5mm TRRS connector: Tip is Left audio, Ring1 is Right audio, Ring2 is Ground and Sleeve is Mic +