The thing is, YouTube is an highly intensive data usage application. It require a strong network connection. If you're getting good connection and you're having problem playing a video, then you could try one of the following troubleshooting tips; 1) Go to Settings - applications - manage applications - all, then scroll to YouTube - delete data. 2) Update the data profile on the phone. 3) Uninstall / reinstall updates from Adobe flash player. (You can find this in applications settings as well. Best of luck.