• OnePlus iPhone 6s Case

OnePlus iPhone 6s Case (Photo : Twitter)

OnePlus is now selling a "Sandstone" black case for Apple's iPhone 6 and 6s devices, which includes an invitation inside to buy the OnePlus X Android smartphone. The ceramic Google phone's $249 price tag is about $400 less than the 6s model, and some buyers will get the old iPhone-like handset for free.     

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OnePlus' iPhone case is stronger and sturdier than Apple's official 100 percent silicon cases, according to Tech Crunch. It has a price point of about $20, which would make it a wise choice as a Christmas gift, such as a stocking stuffer.

This year the Chinese company launched its OnePlus 2 Android smartphone during the summer months, and then the OnePlus X model during October. The black iPhone case is the year's third new product.  

One of the main theories about why OnePlus would include the invitation in its iPhone case is near-free advertising. However, OnePlus co-founder Carl Pei shared with TechCrunch that one goal is to give iPhone owners another smartphone choice.

There is some debate about whether OnePlus' invite is a "fair" way to market products. In any case, it is not the first time the company has used fun ways to advertise items.

It is not clear how many iPhone owners would actually switch to the OnePlus X. However, the black smartphone case makes the Apple device easier to grip, and a wily way to advertise its budget phone, according to Engadget.

OnePlus was founded in 2013, and is headquartered in Shenzhen, China. Its goal is to produce smartphones with high-end quality and lower price tags than other units in the same class.