Primary applications of these 4-position, 2.5-mm, surface-mount mini phone jacks is for headsets with microphones, which is now required in many foreign counties in order to use cell phones in cars. The jack (J-2504 series) accepts either a 2.5-mm plug that has the 4-positions in a row or a plug that has 3 contacts on the 4th position for making contact on the outside of the bushing. The advantage of the last configuration is that it offers better resistance to damage when the plug is severely jerked at a right-angle to the jack. The J-2504 is rated at 10k life cycles and has the added feature of switched contacts for the tip and ring to allow the application to switch the output from internal to external. The jack costs under $0.30 each in volume and can be shipped in bulk or on tape-and-reel.