1. Are you using YouTube - Broadcast Yourself.
? If there is a chance of it working on your OS version, that is the URL you need to use. I can't remember back that far whether I was using it on 4.2 or even 4.5.
Check the forum for your series and the latest OS thread at the top. I know you psoted at crackberry as well, so check the latest OS threads there too. As far as best, I don't know.
Some advice: Make sure ahead of time you are prepared to downgrade if you aren't happy. You will lose some free memory and you may notice a performance hit. You may want to go back.
2. There are not device specific versions of Desktop Manager. The latest version should work with old devices, so far as I know. But if you do want to use an older version, there is a sticky thread here on the board with links. Just search.
However, you need to troubleshoot problems connecting to the device. There is a sticky thread here on the board and also a KB article on blackberry.com. Again, search and you will find them.
3. I know AT&T hides, or at least in the past hid BlackBerry Maps. That may be your issue. I'm not the best to advise on this. See what others say. In the mean time, once you get Desktop Manager working for you, make sure BlackBerry Maps is installed, and then make sure the icon is not hidden. I believe if you've been able to activate the device on T-Mobile and get the service books, then you should have BlackBerry Maps, but I don't know. Posted via BlackBerryForums.com Mobile