broken screen replacement question

I dropped my 3G-S two weeks ago, broke the screen.
I went to an Apple store hoping the genius would feel sorry for me and replace it, but he ended up trying to charge me $199 and told me they don't replace them (even though I've had friends who've gotten theirs replaced free of charge).

So I got on ebay and bought a new screen and replaced it myself. The phone is 100% fully functional now. The only problem now is that when I opened it, I guess I must have messed with something and the silence switch on the side of the phone is extremely sensitive and sometimes it goes off silent by itself when it's not even touched.

I checked my warranty status online on apple.com and it still says my device is under warranty, so I'm guessing the tech didn't void it? I got an appointment at a different apple store tomorrow to try and see if they can just replace my phone since the screen isn't broken.

I was wondering- do these techs keep notes of every single appointment made, and if they do, is it only at that apple store or do they make it global? I can see my repair history on apple.com but it only shows the times when my phone was replaced.

Hopefully I can get a replacement. If the genius tells me my warranty is void because of a broken screen, he can clearly see the screen isn't broken right? Do you guys think I'll have any luck with this? Thanks!