Deluxe Hands-Free Headset for Wireless, Cellular and Cordless Phones. The Contact-501 is a comfortable and adjustable headset for optimized stability. It is compatible with most wireless and cellular phones using standard headset plug (2.5mm) or included connectors and works with cordless home and office telephones with 2.5mm jack. Unobtrusive noise canceling microphone filters out background noise for supreme voice clarity (NCAT2 exclusivity). Microphone boom firmly holds position and can be worn on left or right side.