The deal is this -- you can buy a 16GB iPhone 4 for just $149, which is $50 off the price that you'll find at Apple or AT&T stores, and much better than even picking one up at your local Walmart. That price, of course, requires a minimum 2-year commitment to an AT&T plan.
The 32GB iPhone 4 is similarly priced at $249, and an 8GB iPhone 3GS is an absolute steal at $49. In addition, if you have a working and non-damaged iPhone 3G, you can get a $75 trade-in credit. A 3GS will get you a whopping $125 trade-in.
You can only get this deal by walking into a Radio Shack location, and this is only good through Saturday, December 11. Grab that old 3GS and get movin' to "The Shack" before it's too late.