Radio Shack has kicked off a special iPhone offer: Trade in your iPhone 4S and get an iPhone 5S free, or sign up for a two-year wireless contract and get the iPhone 5S (16GB) for $100.

The promotion, which began Friday, is available online and offline. The traded phone cannot have any cracks. The deal's fine print notes that the appraisal promotion is good through June 7 but it does not specifically state when the promotion ends.

The news comes just a little over a month since Radio Shack announced it would be closing 20 percent of its locations, about 1,100 stores, due to a poor holiday season in which its net loss tripled, according to one report.

In making the store closing announcement company leaders said it was a matter of having to many storefronts for viability. The retailer has 5,200 locations through the U.S. and states that 90 percent of the population lives within minutes of a store. The store employs 27,500 workers nationwide.

At the time of the announcement Radio Shack did not release a list of locations to be closed.