T-Mobile seems to be on track to refresh its Windows Phone 8 (WP8) smartphone portfolio. A recent T-Mobile internal document suggests that the entry level Nokia Lumia 521 will head to the carrier on April 24 and it will be game over for the Nokia Lumia 810 and the HTC 8X.

T-Mobile launched the WP8-powered Nokia Lumia 521 at the Mobile World Congress (MWC) event earlier this year and per the leaked T-Mobile internal document, the smartphone will reach retail stores on April 24, which is the same date when the carrier plans to start shipping the latest Android-powered HTC One.

The Nokia Lumia 810 and the HTC 8X are among the first smartphones to run on Microsoft's latest WP8 software. Launched in November 2012, both the handsets are relatively new not only to T-Mobile but to the smartphone industry. The Lumia 810 and the HTC 8X are both mid-segment handsets and it's interesting that an entry-level smartphone such as the Lumia 521 is replacing not one, but two mid-segment phones on the carrier.

"As for this morning's story about the sudden disappearance of both the Lumia 810 and Windows Phone 8X from T-Mobile's website, we've solved 50% of the mystery. According to the same planogram that outs the 521 release date, the 810 is set for EOL (end of life) in 'May.' That could be the reason T-Mobile has removed the item from its website prematurely, its either out of inventory or not interested in ordering any more. It's speculation as to why it was removed now as opposed to sometime in May, but it's clear the Lumia 810 has run its course," reports Tmo News.

The Lumia 521 is T-Mobile's version of the Lumia 520 and includes similar specifications such as a 4-inch 800 x 480 display, 512RAM, 8GB storage with a microSD slot, 5 megapixel camera with 720p video recording, 9.9mm thick and HSPA+ 21Mbps connectivity.

The Lumia 521 will suit smartphone buyers looking to experience a WP8 smartphone at an affordable price.