Recently different standardization bodies have joined to create a new standard to open network API between the telecom service level, which gives connectivity to different networks, and the application level, which is built by enterprises outside the telecom network domain.This OSA (Open Service Access) API is a standard interface for applications to use the capabilities of a network without knowing technology details. Parlay/OSA [4] specification covers different aspects: messaging, location, conferencing, security, call-control, etc.Our work focuses on the Call Control API specification whose main goal is both to allow applications creating whichever kind of call between voice terminals connected to different networks, and also react to call requests coming from various networks, according to the service-logic implemented by the applications (e.g. [3]).The Parlay documentation provides a specification of the Call Control Service Capability Feature (SCF) aspects of the interface by means of UML [5] class, state, and sequence diagrams. However, although UML emerges as the best practice modeling notation for object-oriented software development, in its current setting it still lacks of a formal semantics. As a consequence its usage and, correspondingly, the interpretation of developed models may differ considerably. For this reason several of semantics models for UML diagrams have been provided (see for instance [1]). We present a methodology to produce an ASM specification of the Parlay call control from the UML diagrams provided in the documentation.