LOL! It's funny you say your friends can't even tell and don't believe you. I think the suggestion of Siri is a GR8 one. Show that to them and they will shut the F up.
Everyeone here at work knew I was getting this phone and they knew it looked like the iPhone 4. But to be sure one guy said, let's ask Siri a question. So I fired her up and they knew I really got it.
It's not so bad concerning yourself as to what your friends think of you. Friends are important to some people while not so important to others.
If you have a 64Gig iPhone 4S show them that. That would shut them up too, but Siri is the surefire way to let them know you're not playing around, and yes, this is an iPhone 4S.
I personally don't mind that it looks identical to the iPhone 4. That way, people who shouldn't know that it is the new iPhone, won't. They'll think you just have that old "sh*t". (In my neighborhood, that's a good thing. Oh, they are so tech savvy that they know an old iPhone is pretty much worthless, but the new sh*t is the one you wanna get from someone. No one ever said criminals are geniuses.)
When I went to the Apple Store for a swap out, that I didn't get, the Genius asked me if this was the iPhone 4 when he looked at it. It's masked in the old coat. I like that a lot.