The desire within the telecommunications world for new and faster business growth has been a major drive towards the development of open network APIs. Over the past 7 years several (semi) standardization groups have announced to work on network APIs, including TINA-C, JAIN, IEEE P1520, INforum, 3GPP, JAIN, Parlay. The Parlay group seems most successful in attracting industry awareness with their API, called the Parlay API. The rational behind the Parlay API is that it attracts innovation from third parties that are outside the network operator's domain to build and deploy new network hosted applications. This also means that the public telecom network is opened for niche and short-lived applications as well as for applications that possibly integrate telephones with other terminals such as PCs. The Parlay group has successfully passed the first two phases of success, namely publishing their API on the right moment in time and attracting a critical mass within the telecom industry with their results. Prototyping the API on a real network execution platform is the only manner to show its technical feasibility. Such an exercise was executed internally within Lucent Technologies and raised a number of questions as well as recommendations on both the technical and the semantical behavior for systems that will be interconnected via the Parlay API. In this paper we share these results, showing drawbacks , advantages of as well as challenges for this API.