Abstract-Interoperability among telecommunications systems, possibly by different vendors, is essential for both the development of many telecommunications networks, and today's civilization development. Interoperability testing is very costly, as it has a complexity of (n**2) for n systems, and somewhat informal. In this paper, we develop a 'Conformance Testing (CT)'-based formal technique to determine interoperability requirements/guarantees. It allows automated derivation of the interoperability' requirements of various networks as well as the interoperability guarantees among different telecommunications systems. This is achieved using static analysis of the conformance classes of the standard and knowledge of the implementation's degree of conformance (DoC) of the telecommunications systems. Consequently, it results in a lot of cost saving in addition to being a formal technique.