Apple CNETiPhone3G16GBBlack User Guide - Page 137

Sound, Music, and Video No Sound  Unplug and reconnect the headset. Make sure the connector is pushed in all the way.  Make sure the volume isn't turned down all the way.  Music on iPhone might be paused. Try clicking the mic button on the headset to resume playback.Or from the Home screen tap iPod, tap Now Playing, then tap .  Check to see if a volume limit is set. From the Home screen choose Settings > iPod > Volume Limit. For more information, see "Music" on page 117.  Make sure you are using the latest version of iTunes (go to www.apple.com/itunes).  If you are using the optional dock's line out port, make sure your external speakers or stereo are turned on and working properly. Clicking Mic Button Doesn't Resume Music Playback iPhone goes to sleep after music has been paused for five minutes. Press the Home or Sleep/Wake button to wake up iPhone. Headphones Don't Fit In Jack iPhone supports third-party headsets and headphones with a standard 3.5 millimeter stereo miniplug. If you have an original iPhone, some headsets and headphones may not connect properly to iPhone because the plug body is too large to fit in the jack inset. Third-party adapters may be available. Song, Video, or Other Items Won't Play The song may have been encoded in a format that iPhone doesn't support. The following audio file formats are supported by iPhone. These include formats for audiobooks and podcasting:  AAC (M4A, M4B, M4P, up to 320 Kbps)  Apple Lossless (a high-quality compressed format)  MP3 (up to 320 Kbps)  MP3 Variable Bit Rate (VBR)  WAV  AA (audible.com spoken word, formats 2, 3, and 4)  AAX (audible.com spoken word, AudibleEnhanced format)  AIFF The following video file formats are supported by iPhone:  H.264 (Baseline Profile Level 3.0)  MPEG-4 (Simple Profile) Appendix A Troubleshooting 137