Just picked up my iphone 4 last week. I picked up a bumper, because I never use ANY phone without a case, and guess what? I can make phone calls and receive them, and don't use any signal, yahoo!
Oh yea and my bumper'd iPhone 4 doesn't slip off of a diagonal surface!
Oh yea and my iPhone 4 has no problem with it's sensor!
Oh yea and my iPhone 4 feels solid, not cheap and plastic like the iPhone 3G/s!
Oh yea and my iPhone 4 is plenty comfortable to hold!
Oh yea and my bumper'd iPhone 4 doesn't lose signal at all!
Oh yea and I was fine with my 3G until I realized that the iPhone 4 is superior in nearly every single way!
Not to mention..
Oh yea, my iPhone 4 has a crisp, clear screen (not blurry compared to the 3Gs), better camera, video and still, can use iOS4 without slowdown, my battery lasts FOREVER, AND:
I am able to get this:
http://www.speedtest.net/iphone/42709716.png
Can your 3GS do that?