Microsoft revealed on Wednesday that it has delayed its Windows Phone 7 release of Angry Birds.

The software giant had previously promised that Angry Birds would be made available on May 25. Joe Belfiore, who oversees Windows Phone Program Management, proudly announced at MIX11 last month:”Angry birds, i’m excited to tell you and everyone else who’s following on the Internet, will be available on our Marketplace on May 25.” Unfortunately Redmond has delayed the release to June 29. Microsoft says the delay is down to a better experience. “The shift in timing of “Angry Birds” as the final title in the Must Have Games lineup was a decision made to ensure we provide the best possible gaming experience on Windows Phone,” said a Microsoft spokesperson.

Rovio previously confirmed that Angry Birds was on its way to Microsoft’s new mobile platform in February. Rovio’s Peter Vesterbacka blamed the delay on Microsoft’s legal team. “Let’s just say, Microsoft has a lot of lawyers,” he said. Microsoft originally ruffled the Angry Birds’ teams feathers when they accidentally posted an image suggesting an Angry Birds Windows Phone 7 app was on the cards. Rovio originally said ”Microsoft put the Angry Birds icon on their site without our permission.” Microsoft responded to the tweet claiming the image was a mockup, not meant to go live and that the Angry Birds icon was included by mistake.

The addition of Angry Birds for Windows Phone 7 is confirmation that the platform is slowly going mainstream. Angry Birds is one of the most popular iPhone apps and has recently been ported to Google’s Android OS. Microsoft is planning an updated version of Windows Phone, codenamed “Mango”, for release in the second half of 2011. Mango will introduce improved multitasking and faster resume times for games like Angry Birds.

Thanks to WinRumors reader Ryan for the news tip