How to replace the antenna

I have an HTC inspire that gets sucky reception in my house. Sometimes it works ok and other times I can't connect at all. I think it's an antenna issue because my wife's iPhone never has a problem and she can walk all around the house and still talk. With my phone if I don't hang by the front window my calls frequently get dropped. We both use the same service so you'd think we'd get at least comparable reception.

So is there a better antenna on the market than the original?