User trials for future mobile telecommunication applications inherently pose several particular challenges which are difficult to meet in a traditional lab environment. In this paper we describe LiLiPUT (Lightweight Lab Equipment for Portable User Testing in Telecommunications), a highly flexible wearable test system which has been realized as a fully operational prototype at the Telecommunications Research Center Vienna (ftw.). Then we illustrate how we use LiLiPUT for testing various types of mobile application in the wild. Keywords Mobile usability, mobile HCI, wearable lab equipment ACM Classification Keywords H5.m. Information interfaces and presentation (e.g., HCI): Miscellaneous.