Prepaid Cell Phone for Expats in Costa Rica?

I am a perpetual tourist, age 51, retired, widowed, moved to Costa Rica from Los Angeles, California last April 2010. I use Skype on my Laptop to make calls any where I want. But I am now establishing friends here in Costa Rica and they cannot call me. I know a tourist cannot own a phone line. But what about prepaid phones? Is there a prepaid phone I can buy and use my credit card to load minutes from month to month until I decide to become a resident? Thanks for all responses. Pura Vida from La Fortuna!