Some manufacturers get a slice of Microsoft's revenue from Bing
The Windows Phone Dev Center currently reminds those manufacturers that have an agreement with Microsoft, how to enter a code needed so that they can share search revenue from Bing. There is nothing new about this. Google has a similar arrangement with some manufacturers of Android phones.
Over the last year, we have seen a number of handset manufacturers issue low priced Android phones in Asia. Now, with Windows Phone 8.1 offering more features, manufacturers in the region are building low priced Windows Phone 8.1 powered models. With the pricing on these phones leaving a very small profit margin, any percentage of Bing search revenue and Windows Phone Store revenue that these manufacturers receive, is a welcome source of cash that allows them to sell Windows Phone models at a "value" price.
source: WindowsPhoneDevCenter via WMPoweruser