sorry if this overlaps other threads but i thought i'd put all my info in one tidy post. these may be of some help to someone?: 1. Power button not responding. my power button suddenly stopped responding. i find if i apply a moderate amount of pressure to the screen just below the power button, in the black area just OUTSIDE the actual display and press the power button i can finally switch off my 3GS. 2. poor GPS performance. for about a year my 3GS's GPS capabilities were great. i used CoPilot all the time and the start up was far quicker than my TomTom. initially i thought the iOS4 update killed my GPS as it suddenly became too unreliable, even in open skies. recently i found that one re-seating the gold tabs inside the phone dramatically improved the GPS performance - maybe just a coincidence but worth a try. the gold tabs are located underneath the screen on the lower right hand side. they should both be touching the metal chassis that runs around the phone. (see youtube for screen removal - you don't need to disconnect anything, just lift it enough to get a plastic tool in there and bend them a bit). 3. interference - that galloping, morse-code type interference, like when you're phone's too close to a speaker. i was getting it when making/receiving calls. again this is down to the gold tabs not making good contact with the chassis. a gentle bend as above should sort this. these may not solve everyone's problems. (if you're not sure what you're doing take your phone to someone who does). but i hope it's useful to someone?