it is against most carrier's ToS to use tethering without a tethering plan, but i'm on Net10 and while they explictely say 'NEVER use tethering on Android' on their Smartphone packages, the worst they ever did to me was slow my speed to dial-up (or 56Kbps) if i went over a 'daily limit' which apparently is set at 2GB/day or 1GB/month total use. however no actual app worked except for one--wifi tether for root users--not sure why but none of the others worked unless you wanted USB only. some froze at the 'setting up tether' stage or just booted me back to my home screen, or told me it was not possible. i would advise never to get into a habit of using this method or replacing your current internet service, and it will not work with online gaming (latency issues) and if using Netflix it will work for one day and then you get dial-up speeds, but for a backup to your main internet when it goes down, or using it when out and not near a wifi hotspot somewhere, for browsing the web or checking email or weather, it is fine.
