Microsoft unveiled a bunch of great stuff at their Build conference yesterday morning. One of those things is the forthcoming Windows Phone 8.1. The new feature packed OS will debut in a variety of handsets worldwide. The first such handset to debut in the United States is the Lumia 635.

The Lumia 635 will deliver an uncompromised Windows Phone 8.1 experience with fast quad core processor, bright colorful design with changeable shells and 4.5″ ClearBlack screen. It will also feature lightning fast 4G/LTE. Nokia says that the Nokia Lumia 635 will feature “The same experiences as high-end Lumia smartphones including SensorCore with Bing Health and Fitness, Microsoft Office, Nokia Camera, free Nokia MixRadio streaming, and free Global maps and navigation from HERE, which save time and money” The Lumia 635 will also feature Microsoft’s new assistant, Cortana, their competitor to Apple’s Siri.

“The Un-carrier’s all about removing crazy restrictions and delivering total wireless freedom and flexibility,” said Jason Young, senior vice president of Marketing at T-Mobile. “With Windows Phone, we can offer customers another great choice in mobile platforms. And we’re excited to bring to both T-Mobile and MetroPCS customers the combination of next-gen software, great features and fresh design that Nokia’s latest Windows Phone has to offer.”

The Lumia 635 will build on all the qualities and benefits that made its predecessor – the Lumia 521 – so popular among American wireless customers. According to T-Mobile US, first-time smartphone buyers were particularly drawn to the Lumia 521 for its extraordinary ease-of-use and its budget-friendly price point, making it the best-selling Windows Phone device ever for T-Mobile.

“With all the advanced features the Lumia 635 has to offer – like its quad core processor, beautiful 4.5 inch screen and most advanced Windows Phone OS – we fully expect Nokia’s latest smartphone to do as well or better than its predecessor,” Young added.

We can expect the Lumia 635 later this Spring at T-Mobile and MetroPCS retailers.