Microsoft announced today that it will bring a Windows Phone 7.5 update to existing handsets in April. Codenamed Tango, the update lowers Microsoft's minimum specification for Windows Phone and introduces some new features to existing devices. We got an early hands-on look at several builds of Windows Phone today, all of which include new MMS features and several restrictions for devices with 256MB of RAM.

Microsoft is removing background agents with Windows Phone Tango if a device has 256MB of RAM, meaning certain background tasks will not work. Microsoft believes around 95 percent of existing applications will work fine on 256MB of RAM, but the company is encouraging developers to test their applications and is undergoing a testing process of existing Marketplace apps. Windows Phone users will also be warned in applications or in the about screen of their device about limitations from using a Tango device. SkyDrive automatic uploads and Bing Local Scout have both been removed from devices with 256MB of RAM too.

Despite the removals on low-spec devices there's some additions for Windows Phone. MMS has been greatly improved and will now handle video and multiple images as well as a new voice notes feature to record one minute audio snippets. We tested the video feature and noticed that larger MMS videos will error out without a way to trim them, something we hope will be improved by April. Overall the feature bumps in Microsoft's latest Windows Phone update are fairly minor, but the engineering to get its near-entire operating system running on just 256MB of RAM is admirable. The updated MMS features will make their way to existing devices, but the only question is how long will it take for carriers to supply them?

Update: We are checking with Microsoft to confirm whether background audio apps do not run with 256MB RAM devices.

Update 2: Microsoft has confirmed it "misspoke" during our meetings on 256MB of RAM Windows Phone devices. Background audio is still supported on these device types.