The comments on this page are promising for the yellow issue - http://www.tipb.com/2010/06/24/explanation-fix-iphone-4-yellow-splotch-problem/
Cover all of them, regardless of where you bought it (unless it was abroad).
So I could call my nearest Apple shop and arrange to walk in and exchange it?
Yeah, or book an appointment online![]()
Say for example I had an iphone 4 bought from orange (and therefore locked to orange), if I then got that replaced by apple, would the replacement also be locked to orange?