Question about Phone as Modem Tether vs. Wifi Tether

[Cryt]

When connecting my Evo to a computer, there is an "Internet Sharing" option. I am curious to know, does this cost extra monthly? I know the wifi tether is the extra $30 a month, but will this charge me the same?

I only have interest in rooting my phone if it's the only way to share internet with my Netbook. Wifi isn't all that important to me, and seeing as I've completely and utterly failed at doing the Unrevoked method for rooting... I'm hoping I won't actually have to root my phone after all.

 

[sitlet]

Im not entirely sure, but with most phones from Sprint, they will charge you if you tether via usb a lot. I only use it rarely, like once or twice a month, so I never get charged. I'm new to Android, so I'm not sure if they can actually tell you are tethering or just using data on your phone.