Hello there sokkersweety17,
1) Possibly. We use 2 different types of cell technology, CDMA and GSM.
Your version of the Storm 2 may be a CDMA device, the 9550, but if you have the 9520 then its a GSM device and will work on our service. You can also tell which version you have by whether or not its got a slot for a SIM card. If it does, then its compatible with our network and you can use it on any of our Monthly 4G plans.
If you find that yours is compatible, it will need to be programmed to work with our network. Here's instructions for that.
2) UMA is only available on T-Mobile devices at this time. Wifi works independently of your cell phone network, so if your phone has WiFi it can connect to WiFi networks near you regardless of what cell service you're using.
Hope this information answers your question.