If a card dips below a minimum dollar value, Starbucks will automatically refill it from your credit card or debit bank account.

FORBES: The Overachievers: Starbucks Delivers

Google will also offer its own prepaid card, but it requires a credit card to setup and refill.

CNN: Mark Milian

Adding to monthly balances is accomplished by buying Refill cards or by registering a credit or debit card or PayPal account online at CommonCentsMobile.com.

ENGADGET: Common Cents Mobile becomes Sprint's latest prepaid brand, exclusive to Walmart