iPhone 4 Serial number

Water damaged and wont turn on. Been this way for a few months so there is no hope for it.

I know there is one on the sim tray, but the guy at the peach mac store couldnt do a $149 out of warranty swap because the little "plastic tab" next to the battery with the serial number on it (I guess its a second location to confirm the sim tray serial) is missing??

Is there any other location for the serial number? He said he couldnt go by only the sim tray because that is too easy to swap out. I really need to replace my phone :(

Thanks in advance