We are with Internode. Have been with them for about 7 years. Great plans to choose from. We have our phone through them as well with VOIP phone (18c per call to any landline in Australia).
We have never gone over our limit, but DGS is about to start Distance Schooling and we may need to upgrade our plan then.
If we go over the limit, there is no extra charge but the download rate is slower