Why can't I start using a $30 plan?
You can. You just have to pay off your outstanding tab. I'm thinking you bough a phone and you took a TAB of $500 which meant you would only be able to choose from selected plans. If you paid more up front for the phone you would have access to a greater selection of plans. You still can but as I said you'd have to pay off your current TAB. You can do that online on koodo's site.
Chris has it exactly right. With Koodo you have to choose how you want to do things. If you want a high end phone for a low up front cost, you choose Tab Large. This also means your going to have a higher monthly bill, because your getting $500 off of a phone. If you want a lower monthly plan, you would have to pick Tab Small or Medium, which means youll get a great monthly rate plan, but in turn, you have to pay more up front for the phone. And one thing to keep in mind is that with the $30 plan you mentioned, you must be on Tab Small, as that plan isn't available on any other tab levels.