On Tuesday, Apple Inc. launched the sale of 'unlocked' (SIM-free) models of the iPhone 6 and iPhone 6 Plus via its online stores in the United States.

In a post on its official website, Apple stated, "The unlocked iPhone includes all the features of iPhone but without a wireless contract commitment or a carrier installment plan. You can activate and use the unlocked iPhone on the supported wireless network of your choice, such as AT&T, T-Mobile, Verizon, or Sprint in the United States."

A report by IBTimes says that the prices of the latest SIM-free iPhone 6 and iPhone 6 Plus versions are similar to that of the unsubsidized versions of the devices. While the 16GB model of iPhone 6 comes for $649, the 64GB and 128GB versions cost $749 and $849, respectively. The model number of the unlocked iPhone 6 is "A1586."

On the other hand, the 16GB version of the unlocked iPhone 6 Plus costs $749, while 64GB and 128GB versions of the device are available for $849 and $949, respectively. The model number of the unlocked iPhone 6 Plus is "A1524."

IBTimes says that Apple has launched the unlocked models of its latest iPhones at a time when there are rumors that the Cupertino-based technology titan may relaunch the 4-inch iPhone in 2015. The purported iPhone model may be christened "iPhone 6s mini."

Meanwhile, Feng, a Chinese news website, claimed on Monday that Apple did not have any plan to revert to the smaller 4-inch form. Quoting sources in the company's supply chain, the report added that Apple has not begun any new "production tasks" for the purported 4-inch iPhone model.

However, Timothy Arcuri, an analyst at Cowen and Company, issued a note to investors in December 2014 asserting that Apple has been working on a new 4-inch iPhone, which may be launched in 2015.