The antenna of the iPhone was never "fixed". It was a non-issue that was blown out of proportion and forgotten. It was a great parlor trick however, putting it in the Vulcan death grip and watching the bars drop, but that's about it. Not an issue in the real world use of the phone. The new phone is just fine and doesn't need "fixing". I've got a black one and it's an excellent phone. Go out and buy yourself one and enjoy.
I was having the same - Although I would lose signal and had to power cycle the phone to make it search for signal again!
I took it into the Apple Store, and it was exchanged, just like that. Now its working better.