Microsoft is starting to open up a bit on what Windows Phone 8 users can expect with the next version of its Windows Phone 8 operating system, known as "GDR2."

On May 14, company officials shared a couple of the expected GDR (General Distribution Release) 2 features in a blog post that was primarily about the new Lumia 925 phone that Nokia unveiled today. That phone, codenamed "Catwalk," is due out in June on Vodafone and some time after that on T-Mobile. It is Nokia's first lighter-weight, aluminum-body Lumia.

Microsoft's supposed plan, according to my tipsters, is to release three GDR updates to the Windows Phone 8 operating system before delivering what we've been calling Windows Phone Blue.

The "Portico" update -- OS build number 8.0.10211.204 -- which began rolling out last year was considered GDR1. The GDR2 update -- which Microsoft officials never actually call GDR2 in today's blog post -- is coming "this summer." GDR3 sounds like it may be timed to arrive this fall . And Windows Phone Blue is sounding from tipsters more and more like a 2014 release.

In today's blog post, this summer's Windows Phone 8 OS update is described as including "a small number of improvements and upgrades." The post said it will be similar in size to the last update, a k a Portico, which included Wi-Fi and messaging improvements, among other new features.

The new update will include support for CalDAV and CardDAV, so that it will continue to work with Google contact and calendar syncing services, officials said. This CalDAV/CardDAV support previously was rumored for GDR2 .

The update will reintroduce support for FM radio (as a feature carriers can opt to support or not) -- a feature which was part of the Windows Phone 7 operating system platform, but which was cut for Windows Phone 8. The update also will make the Data Sense monitoring feature of Windows Phone 8 available for more carriers to support if they decide to do so.

The coming update also will improve the ability to select, download and pin tunes in Xbox Music and improve the accuracy of song information and "other metadata."

"The update includes hundreds of other small quality improvements," according to Microsoft's blog post. There may be some other major features not yet disclosed by Microsoft officials coming, as well, but right now that's all the Softies are saying.

The GDR2 update will be rolling out to existing Windows Phone 8 users starting "later this summer," officials said today.