Yikes! It's a bummer that after initiating the update your phone stopped working. Thanks for trying out the battery in your son's phone (such a clever idea). I would definitely recommend taking this into a T-Mobile store. They'll be able to run some diagnostics on your phone and see what your replacement options are. Once you visit the store, be sure to keep this thread updated so we make sure everything gets handled.
Howdy, magenta2712904! Just wanted to see if you'd had a chance to stop by the store over the weekend. How did everything go? What were the results of the diagnostics or physical exam -- were we able to help get the phone working, or did we order a warranty replacement for you?