Recognizing the need for a notation that would be used in the very first and often informal stages of the development cycle, the International Telecommunication Union (ITU-T) initiated a question on a User Requirements Notation (URN), which will be standardized as the Z.150 series of Recommendations. URN supports the development, description, and analysis of requirements for telecommunications systems and services, as well as for other types of complex reactive, distributed, and dynamic systems. Through a wireless telephony example, this paper gives an over- view of the core elements and typical usage of the two complementary notations comprised in URN. The Goal-oriented Requirement Language (GRL) is used to describe business goals, non-functional requirements, alternatives, and ra- tionales, whereas Use Case Map (UCM) enables the description of functional requirements as causal scenarios. This paper also briefly explores methodology elements and the complementarity between URN and the existing ITU-T languages.