Just a week ago, Microsoft launched a limited-time trade-in promotion, allowing users to get a minimum $200 gift card for trading in an iPad at one of Microsoft's brick-and-mortar stores.

This week, Microsoft has upped the ante on trade-ins involving its competitors' devices. Users can trade in a variety of phones, tablets and PCs, including Apple iPads and iPhones, Samsung devices, BlackBerry phones and more and receive a gift card worth up to $350 via a new Microsoft Corporate Buyback promotion.

(I'm not sure if Microsoft just launched this program today, September 18, which is the day Apple launched iOS7. I learned about the new promotion via a September 18 blog post by a Microsoft technology evangelist, however.)

The frequently-asked question (FAQ) section of the new promotional site says it is open to anyone. (All that is required is a Microsoft Account ID, which anyone, including non-Microsoft employees and non-Microsoft users can obtain for free.) There also is a way for businesses to trade in multiple devices simultaneously and get a single quote for the value of those devices.

The amount that users will get is calculated via a deal Microsoft has with Clover Wireless, which is a company that provides private label trade-in, buy-back and repair services.

Here's how the new promotion works, as described on the FAQ page. Users enter the details of any devices they want to trade in. Clover Wireless creates an estimate of the value of those devices. Users then register their planned trades and are sent instructions on how to package and mail in the devices using a pre-paid shipping label. Users are required to show a proof-of-purchase of a Microsoft device (specifically, it seems, a Windows Phone and/or Surface tablet), which the users must buy within 30 days of the date when they ship their old devices to Clover Wireless. Within 60 days of receipt, Clover will send users their rebates in the form of a prepaid Visa card.

According to the site, Clover may opt to refurbish the devices users trade in and resell them or donate them charitably.

There's no date I can find as to when the Clover/Microsoft Corporate Buyback promotion is set to expire. There's also nothing I see on the site so far indicating this is open to North American residents only, though I don't see carriers from Europe, Asia or Australia listed in the device registration section of the site.

I have a question in to Microsoft in case there are further details or provisions worth noting.