The T-Mobile Sidekick 4G is actually a surprisingly easy phone to root. There are many phones out there that require you to type in lines of code and download terminal emulators, which is normally far to complex for the average person who's just looking to download a screenshot app or get rid of some of that nasty preloaded carrier "bloatware."
If you don’t know what rooting is, it’s basically the Android equivalent of jail-breaking for the iPhone. Rooting allows you to download and use "root-only" apps from the Android Marketplace (now called Google Play) and gives you access to goodies like overclocking and custom ROMs. More information on rooting can be found with a simple Google search.
1.) First off, you’ll need to download SuperOneClick, an application that will allow you to root your Sidekick 4G. It can be downloaded by Googling "SuperOneClick" and clicking on the first link, then scrolling down past the first image and then clicking "Click Here To Download SuperOneClick v2.3.3" and allowing it to download. I would recommend saving it to your desktop for easy access later on.
2.) Secondly, you need to turn on the “USB Debugging” option on your phone. This can be found by going to Settings > Applications > Development. Select "USB Debugging" and turn it on.
3.) Next, connect your phone to your PC via USB and allow it to install the necessary drivers.
4.) Once the drivers finish installing, go back to the file you downloaded and unzip it if needed. Run the application named “SuperOneClick.exe” and wait for it to load.
5.) Click “Run” and wait for it to give you the option to test to make sure that the root was installed correctly. I recommend doing this, but you may skip it if you wish.
6.) If there was any problems during rooting (unlikely, as this is one of the safest and foolproof methods of rooting), all you need to do is reboot your phone and repeat steps 2-5.
7.) Reboot your phone, and let it sit (don't touch it!) for about 5 minutes to let everything settle. Enjoy your freshly rooted Sidekick 4G.