Apple on Thursday unveiled the next major version of its desktop operating system, OS X 10.8 Mountain Lion. The new operating system for Mac desktops and notebooks will feature a wide range of changes from new apps to redesigned visual elements, but one of the most highly anticipated features Apple unveiled was iMessage integration thanks to a new Messages app that will replace iChat. Apple released a beta of its Messages app to users running OS X 10.7.3 Lion, but French blog Consomac on Friday discovered that Lion users will only have access to the new app during the beta period. “Thank you for participating in the Messages Beta program. With the inclusion of Messages in OS X Mountain Lion, the Messages Beta program has ended,” a text string within the app’s resource files states. “To continue using Messages, please visit the Mac App Store and purchase OS X Mountain Lion.” Apple’s OS X 10.8 Mountain Lion upgrade will be available this summer for what will likely be a $29 fee, but a number of recent Intel-based Macs will not support the new OS, so these users will not have access to Apple’s new Messages app.