OSA defines standard APIs for applications so that users can access services provided by other vendors products. The standards for OSA are being developed as part of the 3rd Generation Partnership Project (3GPP). The standards for OSA are published by ETSI and 3GPP. The API for OSA is called Parlay, (or Parlay/OSA or OSA/Parlay)
OSA is based on results of the RACE I project ROSA, which proved the feasability of an architecture that would make services design, service deployment, and service upgrade more structured and more cost-effective than with existing approaches.
"Open Services Architecture is the road to enterprise" - Bill Gates - Infoworld Mar 2, 1992