Abstract: A device to be used with a mobile station, comprising a body to be attached e.g. to a belt with an attachment plate and a fastener attached to the mobile station with a fitting piece. The body includes control flanges bent inward from two opposite sides and from below to guide the fastener which comprises a neck and a wider end consisting of a flange placed behind the guide flanges. The body also includes a projection or a similar structure acting against a spring force, resisting the upward movement of the fastener when said fastener is in the locked position.