Here is the link... HotSpot @Home (UMA) is not working on my BlackBerry Curve 8320
You have to go to it from your phone!!!
However, I doubt that it will work as your 8120 needs special hotspot@home firmware that basicall makes it a t-mobile phone. Where did you get the 8120? When you boot it up does it show as being a T-mobile phone with the T-mobile hotspot@home splash screen?