Ever since I upgraded my iPhone 3G to OS 3.1.2 I find I cannot "slide to answer" calls or "slide to view" text messages. When my phone is asleep (screen off) and either someone calls me or I receive a text, I get the usual "wallpaper" screen with either the blue box showing me who's sent a text or the indication of who's calling. However when I try to slide the bar at the bottom to either view the text message or answer the phone, it is totally unresponsive. The only way to make it respond is to put the display to sleep (press the lock button on the top of the phone) and wake it up again (press the home button), then the slider will work. This obviously is totally unacceptable when someone's phoning, as it hangs up on them, and I then have to call them back, which on PAYG isn't ideal. How can I fix this? I don't believe I have an older version of the iPhone OS on my computer as I got a new MBP after I last upgraded the OS.