Currently Being ModeratedDec 28, 2012 10:24 AM (in response to nadabush)
Most likely it is the LCD Display or possibly but less likely Logic Board fault. If the iPhone has Warranty or AppleCare, make Genius reservation or set up Service and take or send to Apple for resolution. If no coverage the first step would be replacement of the Front Screen Assembly (Front Glass, Digitizer, LCD Display) for iPhone 4S. If you want this done at Apple, it is $199 for replacement iPhone 4S exactly like yours.
Currently Being ModeratedDec 28, 2012 10:59 AM (in response to brad805)
I seriously doubt that the problem is with the lcd screen because i see this lines only when I touch a function in the settings menu, when I'm using safari or watching videos or writing a message I don't see any lines, plus this line started to appear only after I upgraded the firmware to iOS 6