also i need to know the least amount of units you can buy

You can find the TracFone cards at Target, WalMart or Walgreen's and they are available in 30, 40, 50, 60, 100 minutes....I think there are other increments too. You can also buy the 1-year service card....that will guarantee your service isn't deactivated during the year. Hope this answers your question....

There's a Retailers section on Tracfone's website. Also you can get airtime online at all the airtime stores, ranging from prepaidwireless.com to BabbleBug to CheapPhoneCards etc. However if you want the cheapest card, go to Tracfone's own website and buy the $9.99 30-minute card. Yes, you'll have to pay tax but it's still cheaper than other people charge...though you could look at PINExpo or TeleComServices also...