Last night, i put some ringtones into the iPhone and listen to them. Suddenly, the speaker is muted. I didn't do anything. Then I turned off and on again, still no sound. Even i reset everything or restored the firmware. Does anyone have the same problem? I brought it to the store to have warranty. The thing is it happened just 2 hours right after i bought the phone, haven't made any phone call yet or install application, nothing. Thus, i demanded to have a replacement but they refused.