Problem with iPhone 4 model A1332 wifi

So I have a regular iPhone 4 model A 1332 that I have owned for over a year now. Not too long ago, my iPhone stopped picking up wifi unless I was ten feet from the router. I have the latest soft ware ( iOS 5.1.1) installed on my phone. The wifi used to work flawlessly but now will hardly pick up anything. I have tested my friends iPhone 4s model A2380 against it , his will pick up 5 routers, mine ZERO! I almost threw mine out of the window of a 15 story building after that. Can I go to an apple store and get it fixed or replaced? I have tried turning wifif on and off, power on and off , soft reset, hard reset, factory reset and none haves made a difference in the wifi reception strength. And this is a problem everywhere I go not just in my apartment.