There are kits available for iphone and android phones. So, depending on the type of phone you are currently using then, make sure to buy the correct kit. If the phone is an "old school type of phone" you will need to purchase an android or iphone for the sim card to work.
Therefore, you will need to purchase a iphone or android phone of your choosing (sold at walmart). For $30 a month, you should receive unlimited, talk, text and internet service.