Good news, US-based Windows Phone fans: You'll have a decent new choice just days from now, when T-Mobile gets the Lumia 635, an entry-level Windows Phone 8.1-based smart phone handset that will be sold as the successor to the Lumia 521.

You'll be able to grab the Lumia 635 on T-Mobile in two different ways:

T-Mobile. T-Mobile users can purchase the Lumia 635 from T-Mobile or the Home Shopping Network starting on Saturday, July 5 for $0 down and $7 per month for 24 months (for a total of $168). That cost is for the phone only and doesn't include voice, text or data of course, so you will also need to get a post-paid T-Mobile Simple Choice plan at $40 per month and up. And if I'm reading this right, you could wait until July 16 and get it for a special promotion price of $99 instead. (It's not clear if a voice/text/data plan is required.)

Metro PCS. Starting July 18, the Lumia 635 will be available at a special promotional price of $99.

From a specifications standpoint, the Lumia 635 mixes some good with some bad, but is mostly low-end. It features a 1.2 GHz quad-core Snapdragon 400 processor (good) with just 512 MB of RAM (bad), 8 GB of storage (bad) and microSD expansion to 128 GB (good). The screen is a gorgeous 4.5-inch ClearBlack unit with Gorilla Glass 3 protection (good) but only runs at 854 x 480 (bad), which means it uses onscreen buttons for Back, Start and Search, and not physical buttons (good or bad, depending on how you look at it). The main camera is only 5 megapixels (bad), so it's nothing special.

But it is stylish, and one of the neat things about the 635 is that (like the 520, but unlike the 521) you will be able to replace its color back with a differently colored cover: Matte white and black, and bright yellow, green and orange will be available.

There is one big deal here: The Lumia 635 features Nokia's SensorCore technology, which means it can be used to monitor your fitness activity without destroying battery life. So it will integrate with apps like Bing Health & Fitness and help you measure steps, miles walked, calories burned and the like.

And it does of course come preinstalled with both Windows Phone 8.1 and the Lumia Cyan firmware.