Screenshot by Lance Whitney/CNET

iPhone buyers looking for a healthy discount on a new phone can find one at their local RadioShack store, the company tweeted this week.

The retailer is selling the 16GB iPhone 4S for $149.99, the 32GB edition for $249.99, and the 8GB iPhone 4 for $49, all three a full $50 off the retail price.

The promotion is in-store only, so customers can't score the lower price by ordering online. As expected, the sale price requires the usual two-year contract. Buyers can choose from among any of the three U.S. iPhone carriers: Verizon Wireless, AT&T, or Sprint.

The Web page for a RadioShack store in Connecticut lists the sale as having started May 7 and ending May 31. However, an inside source says the sale will actually last until the end of June. Interested customers should call or visit their local RadioShack outlet for further details.

RadioShack is the second major retailer this week to put Apple's flagship phone up for sale.

Earlier this week Target kicked off its own $50-off promotion on the iPhone 4S and the iPhone 4. Target's sale is slated to last until the end of June.

Updated 8:15 a.m. PT with confrirmation from RadioShack that contracts with all three U.S. iPhone carriers are available.