It is almost like Apple has a magic switch and it flicks it on after about 18-20 months that causes the phone to slow down, so people start thinking about an upgrade even if the don't want to. My iPhone 4 which was fine until recently suddenly seems to have slowed down for no reason. Maps, Safari, opening apps everything seems to take a second or two more. This happened to me with the 3G and it is now happening again on the 4. I haven't done anything to my phone out of the ordinary. I've just been using it like always do.