Development of software for mobile environment is often complicated by difficulty of "real-life" testing. Functional testing could be run against network emulator( s), but this is often not enough for performance testing. The latter includes, for example, testing of response times or quality of end-to-end service. For such tasks, emulation of live network is necessary. This paper describes the inexpensive, easy to use, and fully configurable testing tool, developed at Nokia Research Center. The testbed named COSIME (COmbined SIMulator and Emulator) provides real-life network environment for testing the mobile phone software, from the network-specific protocol stack up to user?s applications.