In the past month, the iphone that I bought in September 2007 has not been receiving calls while it is locked. Sometimes I will receive a voicemail notification hours later, but usually I have no idea someone called me. If the phone is not in the locked mode, then the screen shows who is calling, but there is no ringtone. I have read up on this problem, and many people have had to have theirs replaced. I have an appointment at the Genius Bar this Tuesday, but my question is, how will they handle this if they have to replace it. Will I get a new 3G one, or do they have some old ones? I know the 3G demand is high, so what happens if they don't have any at the time? Honestly I am very happy with my current Iphone except for this problem, and I don't care if it is replaced or not, but I am just wondering about what could happen. Thanks.