This paper discusses development of the technology required to enable location services on Motorola's iDEN cellular phone system. Our approach consists of handset based time difference of arrival (TDOA) measurement. The performance of this system has been determined both by computer simulation and field trials. The overall TDOA system and specific algorithms utilized are described. Performance estimates for numerous special cases are discussed. These cases include highway, in-building, and coverage fringe. Particular attention is paid to the effects of propagation environments (e.g., urban, rural, etc.) on accuracy performance. In addition, bench test and field test performance data is reported and compared to computer simulation predictions