While 2.5mm was the original standard for phone headsets, the slightly larger 3.5mm size is standard for music headphones and is now the more common size on phones. See: Headphone Jack (3.5mm ...

Either size can support stereo sound and/or a microphone, depending on the number of separate connector rings on the plug or jack. Essentially all phones with a 3.5mm jack support a microphone via ...

Some phones offer only a 2.5 mm jack, which is a smaller variety ... Some manufacturers opt for placing a 3.5mm audio jack on this remote control instead of directly on the phone itself.