Walmart will start carrying the phone next week, reports Reuters Bill Rigby.
The 521 sold out in four days at the first retailer to carry it, the Home Shopping Network.
The 521 is a T-Mobile-specific variant of the Lumia 520 that debuted at Mobile World Congress in February. It offers good-but-average hardware for the price (1 GHz dual-core processor, 4-inch touch screen, a 5-megapixel camera, 8G storage expandable to 64G).
However, the phone doesn't require a long-term contract. Walmart will sell it with T-Mobile's $30/month unlimited data and text plan.
If this phone sells well at Walmart, Microsoft may have found a way to attract more users to its Windows Phone platform. The more users it has, the more app developers it will attract. More apps will bring in more users.