mismatch between the iPhone serial number label & the software serial number displayed on the screen.

I'm from Brazil and I had a similar problem. I bought an iPhone 4s directely from Online Apple Store here in my country, and everything was ok until then (serial numbers did match). About five months later I had this problem with the power button and I went to an authorized center and claimed for another device. The service was really fast and good.. in about 3 days I had I my new device (that they gave me wrapped in plastic and out of any box ... but it looked brand new.... is that normal?) . I just took my phone e came home satisfied.

Six months later (still under warranty) my wi-fi just stopped working from day to night. I came back to the same authorized a claimed for another phone and got really surprised when the attendant said "The serial number that is on your phone does not match with the number here in our system" (they had two serial numbers in their system: my first iPhone and the one replaced.. the second was suposed to match, but it didn't) . I told him that this was impossible, cause I didn't leave my phone to any repair or switched to anybody, and explained what happend before. If there was a mistake, it was their mistake .. Nobody checks serial number when receving a new phone (from now on, I will). They probably gave the phone that I was suposed to recieve to another person and I recieved another one, or there was a labeling problem at the factory. When I said that I heard " This is impossible, sir". The fact is that makes me wonder about this new phones that they replace us, are the really new ? But this is as discussion for another topic. How that particular iPhone was with me was a mistery for them and they took it for investigating my problem.

However, now since 14/05/2013 I'm without my iPhone and they are still trying to solve my problem.