Microsoft's Lumia 640 smartphone has been discounted to about $30 at Walmart and Best Buy as an AT&T GoPhone pre-paid package. The cheap phone will include a price cut of about 50 percent from both retail giants, and already be upgraded to Windows 10 Mobile

Lumia 640 includes a 5-inch LCD screen with 720 x 1280 HD resolution, or 294 pixels per inch (ppi).

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The Microsoft phone has a Snapdragon 400 SoC processor with a quad-core 1.2Ghz CPU and Adreno 306 GPU. Meanwhile, it also has 1GB of RAM with 8GB of native storage, and microSD slot allowing a 128GB capacity boost.

Meanwhile, the budget phone includes an 8MP rear camera and 9MP front camera for selfies and video chats. The mobile device gets juice from a 2500mAh battery and runs Windows Phone 8.1 OS.

AT&T's GoPhone pre-paid service has three levels of service. Each plan includes unlimited talk and text, and unlimited messaging to more than 100 countries including Mexico and Canada, according to Phone Arena.

The major carrier's $30/month plan lets customers buy 100MB of data for $5. Next, the $45/month service ($40 with auto-refill) includes 2GB of data and rollover minutes. Finally, the $60/month plan ($55 with auto refill) has 4GB of data, rollover minutes, and free talk/text to and in Mexico and Canada.

In other Lumia news phone owners are still waiting for a Windows 10 Mobile update that was announced in December 2015.

Microsoft has released the list of devices that would get the upgrade, including Lumia 640, 735, 830, and 930. However, there have been no official announcements.

The OS update could be rolled out as soon as next week. That is based on information in a Facebook post for Microsoft Lumia Mexico.

The Lumia Mexico post states that Windows 10 Mobile updates could be sent out as soon as February 29, Monday, according to International Business Times. However, no phone models were listed.  

In addition, there have been false reports in the past. It was wrongly claimed earlier that updates for Lumia 535 and 640 had been rolled out in Latin America and Poland.

Lumia phone sales continue to drop as last month Microsoft reported it sold 4.5 million units during Q4, which was a 43 percent year-over-year slide.