Nokia is at Microsoft's Build developer conference in San Francisco, where it has announced new Windows Phone 8.1-powered smartphones such as the Lumia 630 and Lumia 635.

Starting with the Lumia 635, Nokia said it'll offer high-speed 4G LTE data. The Lumia 630 is a bit different, because it'll land in two 3G variants including dual-SIM. Both phones feature a 4.5-inch ClearBlack screen, 1.2GHz Snapdragon 400 processor, 1830mAh battery, 5 megapixel rear-facing camera with autofocus, and Gorilla Glass 3 display protection.

READ: Nokia Lumia 630 spotted online with 5MP camera 

As for colour options, Nokia said there will be many matte finishes available via changeable shells in the shades orange, green, yellow, white and black. You can also personalise your phone with the Nokia CC-3079, a gloss or matte-finished outer casing available in the colours green, orange, or yellow.

Other features within the new Lumia phones include fitness tracking with an integrated low-power chip called SensorCore, Windows Phone navigation keys integrated into the user interface, a faster social experience with the new Word Flow keyboard, upgraded Live Tiles, the new Action Center, and pre-installed apps like WhatsApp, WeChat, Nokia Camera, Nokia HERE, Nokia MixRadio, etc.

"You’ll also find the latest Xbox games and Internet Explorer straight out of the box for fun, and Enterprise updates that make these phones even better for business with Microsoft Office and OneDrive," announced Nokia in its release.

READ: Nokia Lumia 630 expected at Lumia Build event

The Nokia Lumia 630 is expected to rollout in May for 119€ ($159) for the single-sim variant or 129€ ($169) for the dual-sim variant. It'll land in Asia and Europe first. Meanwhile, the Nokia Lumia 635 will be "broadly available" in July, though it will first release in the US for 149€ ($189).