If you have any Tab owing, just pay that off and you can get the a phone on a new tab
Tab S is a $150 subsidy
Tab M is a $300 subsidy
Tab L is a $500 subsidy
Tab L requires you to change to a Tab L plan and play a $10 Tab L charge monthly (This is the worse deal and I recommend you never get this)
Tab S will work on any new or old plan and there is no extra monthly Tab charge
Tab M is the best deal but your current plan needs to be at least $30 or you can choose an existing plan. There is a $5 monthly tab charge too. As a bonus, if you get the iPhone 5S on Tab M you get an extra $100 off. SO you can bring home the iphone 5S for $275 after paying off any existing tab owing.