The phone jack is a 2.5mm connector with four contacts: stereo + MIC. It is compatible with the headsets used by Motorola smartphones (A780,A1200, ...) and the V-360.
To plug regular (i.e. without microphone) headphones commonly used to listen to music, a compatible 2.5mm 4 rings jack to 3.5mm stereo jack adapter is needed. It has been reported that Nokia's 2.5mm -> 3.5mm adapters do not work, but that a 3.5mm Stereo Audio Adapter for Motorola MPx200/E398 works well, as well as the generic Radio Shack 274-004. You will also want to switch from speaker output to headset, by restoring the appropriate alsa.state-file (usually the mediaplayer should do this for you) or via alsamixer (see below), to enable stereo output in there.
There's a four-ring 2.5mm stereo jack which provides connectivity to old-fashioned wired headsets.
base = ground speaker left (internal impedance 33R) to ground. (+jackinsert detection) speaker right (internal impedance 33R) to ground. tip = mic electret condenser type, to ground. bias (power for mic) 2K2 from +3.3v(wolfson codec) (+HoldButton shortcircuit to ground)
This matches the reported pinout for the Blackberry Pearl  but so far headset compatibility is unconfirmed.
Known working adapters
The headsets used by Motorola smartphones (A780,A1200, ...) and the V-360 have a compatible configuration. The HS-120 (Motorola) works without problems (mic untested).
|Tester||Product||Seller||How it works|
|TimoJyrinki||MP35A||pc-mobile.net||Koss KSC-35 headphones, Altec Lansing inMotion iM4 speakers and car audio via AUX - all work great, if the mixer settings are changed like guided below. One can notice the lack of real quality sound with the headphones, but it's mostly fine for any casual listening. Definitely the output is not ideal/natural because of the high-pass filtering effect from the hardware issue and then artificially boosting low frequencies to compensate.|
Incompatible, but rewireable headsets
The headsets used by some Nokia phones (N95, ...) have the same jack but they are incompatible. For technical information about rewiring them visit Analog wired Headset Nokia. The same is true for Headsets delivered with Sony Ericsson. Here is a short rewiring guide: Analog wired Headset Sony Ericsson.
You probably want to fix mixer settings to overcome the poor low-frequency output, see FreeRunner Hardware Issues for instructions.
To test Headset functionality
- Neo FreeRunner plus April Software Update
- FIC GTA02 battery
- SIM card
- Headset AP