Developers focused on VoIP and messaging applications should take note of a post today on our sister site WebWorkerDaily, about a newly open API from Fring. As more and more open source developers are focusing on software-as-a-service (SaaS) apps online, free ways to integrate VoIP, messaging and telephony tools can add a lot of value. We've previously covered Ribbit's open telephony APIs from this perspective. According to WWD, "the Fring API offers developers the ability to build Fring add-ons, with access to core services like talk, chat, presence, and file transfer." Check it out, although we agree that the iPhone SDK and Google's Android may woo more mobile developers.