YouTube App

• Tap the YouTube icon on your T-Mobile iPhone's Home screen to launch the application. This app provides a portal to the YouTube website, allowing you to search for videos and play them directly on the iPhone's screen. As native YouTube videos -- which you see in your computer's Web browser -- are incompatible with the iPhone, this application is required to view YouTube videos on your device. It automatically opens when you tap a link to an embedded YouTube video in a webpage or application and loads the relevant video.
  
  

Wi-Fi and 3G

• The iPhone's YouTube application is built into the device's iOS firmware. The application, rather than your network provider, requires you to be connected to a Wi-Fi network in order to stream high quality YouTube videos to your iPhone. If you are connected via 3G or EDGE, the quality of YouTube videos is reduced to alleviate strain on the cellular networks and speed up delivery times. Your T-Mobile contract may have a cap on the amount of cellular data you can receive each month, which will be used up at a faster rate by playing manyYouTube videos. Watching over Wi-Fi avoids this problem.
  
  

YouTube Web App

• Although the YouTube application is required to view streaming videos on your iPhone, you can still visit the YouTube website using the Safari Web browser. When you navigate to the YouTube website on your T-Mobile iPhone, the site detects your device and loads the mobile Web application instead. Tapping the "HQ" button will prompt the YouTube Web app to stream a high quality version of the video -- where available -- even if you're connected using the 3G cellular network. Although the quality will be improved, this will use additional cellular data from your T-Mobile contract.
  
  

Public Wi-Fi

• Many cellphone contracts, such as those provided by T-Mobile, include access to public Wi-Fi networks. These are situated in outdoor areas, bars, restaurants, coffee shops and other public venues, allowing you to log in with your contract details to access Wi-Fi Internet while out and about. Check with T-Mobile to find out whether public Wi-Fi access is included in your iPhone contract and use those locations to stream YouTube videos to the device. This provides a fast Internet connection for streaming high quality YouTube videos and does not use your inclusive cellular data allowance.