Ive seen several comments lately of people saying how they are rooted and can tether, implying that you need to be rooted to tether. If your smartphone is 2.2 froyo android comes with it built in. As far as being charged by your carrier, for Tmobile you will only be prompted to add a $15/mo tethering/hotspot plan after 5GB of data, and there are ways around this (change your browser user account). Google has even stated they put nothing in the code to allow carriers to directly control tethering, and they have to outright remove the feature...in which case yea, you'd have to root to run a tethering app.