Mobile World Congress has been dominated by Android smartphones and tablets, plus the Tegra 3 quad-core processor, with Windows Phone hardware coming a distant second in terms of major new device announcements.

Nokia has led the way for Microsoft, showing-off an international version of the Lumia 900 along with the low-end Lumia 610, a phone as important to Nokia as it is to Microsoft. A budget Windows Phone is needed not only as an alternative to cheap Android phones, but also as a device to sell to the next generation of high-end smartphone owners and developing markets around the world.

With Samsung and HTC concentrating on Android at the show, and LG telling everyone that its WP7 device sales have been too poor to consider releasing a new phone, it was left to ZTE to unveil MWC’s only other Windows Phone handset.

ZTE Orbit

Boasting a 4-inch touchscreen with an 800 x 480 pixel resolution, a 1GHz processor and a 5-megapixel camera, the Orbit appears to share the same feature set as several devices in the first wave of Windows Phone releases. But dig down a little further and you’ll find a few differences such as only 4GB of internal memory, plus 256MB of RAM instead of the usual 512MB.

This is because when it goes on sale, the Orbit will run Windows Phone Tango, the next version of Microsoft’s operating system. Except it’s not a new version at all, as the changes are mostly under the surface, so much so that it’ll still be called Windows Phone 7.5.

Windows Phone Tango

Initially, Tango was suspected to be a separate version to Mango entirely, suitable only for low-spec Windows Phone like the Lumia 610 and the Orbit. However, when speaking to PCMag.com, Microsoft’s Greg Sullivan explained that Tango would be a part of Windows Phone 7.5, calling it a “refresh” and that both new and old handsets would see the update.

Tango will provide support for Qualcomm’s 7×27 range of processors and 256MB of RAM, dropping the minimum spec allowed by Windows Phone hardware so low-cost phones can be launched. To ensure the user experience remains consistent, some apps won’t run on devices with 256MB, and multi-tasking will be removed too.

As the update will be applied to all phones, those with higher-spec devices will get a few new features, such as the ability to add more than one picture to an MMS message, plus some overall performance improvements.

Release dates and prices

The ZTE Orbit is due to launch after April, which is also the time-frame given for both the Nokia 610 and the Tango update. However, Theverge.com notes that the software hasn’t been sent for testing with carriers yet, so these dates could shuffle closer to June.

The Nokia 610 has been given a SIM-free price of £160/$250, and it’s reasonable to expect the Orbit to be priced a little cheaper, meaning both will probably dip below £100 on Pay As You Go, or free with a contract.

Remember, Tango, the 610 and the Orbit aren’t being introduced for consumers eying the HTC One X or an iPhone 4S. All this effort is for feature phone owners, youngsters and developing countries, and as we all know, locking customers into an ecosystem early on is very important indeed.