The 3.5 mm TRRS connector for the headphones is located on the top left corner of the device.[57] The headphone socket on the original iPhone is recessed into the casing, making it incompatible with most headsets without the use of an adapter.[58][59] Subsequent generations eliminated the issue by using a flush-mounted headphone socket. Cars equipped with an auxiliary jack allow for handsfree use of the iPhone while driving as a substitute for Bluetooth.
While the iPhone is compatible with normal headphones, Apple provides a headset with additional functionality. A multipurpose button near the microphone can be used to play or pause music, skip tracks, and answer or end phone calls without touching the iPhone. A small number of third-party headsets specifically designed for the iPhone also include the microphone and control button.[60] The current headsets also provide volume controls, which are only compatible with more recent models.[61] These features are achieved by a fourth ring in the audio jack that carries this extra information.
The built-in Bluetooth 2.x+EDR supports wireless earpieces and headphones, which requires the HSP profile. Stereo audio was added in the 3.0 update for hardware that supports A2DP.[51][52] While non-sanctioned third-party solutions exist, the iPhone does not officially support the OBEX file transfer protocol.[62] The lack of these profiles prevents iPhone users from exchanging multimedia files, such as pictures, music and videos, with other bluetooth-enabled cell phones.
Composite[63] or component[64] video at up to 576i and stereo audio can be output from the dock connector using an adapter sold by Apple. iPhone 4 also supports 1024 × 768 VGA output[65] without audio, and HDMI output,[66] with stereo audio, via dock adapters. The iPhone did not support voice recording until the 3.0 software update.