Q: What is the official carrier stand on tethering? (iPhone, M'sia, Maxis, Digi)

It doesn't say any where clearly... so i thought to get some answers here. Is the tethering charge inclusive in the iPhone plans (eg. Maxis) or you do have to pay extra for tethering enabled like in other countries? If you do over the limit (i'm sure this is a cap they are not dumb) what are the additional charge rates?