Make Cheap Calls on Your Cell Phone (PC World)

PC World - Mobile Voice-over-IP services promise to save you money by routing voice calls over your carrier's data network. As more carriers and handsets support high-speed data hookups, such services are proliferating. We looked at four--EQO, Skuku, Skype for Windows Mobile, and Truphone--and discovered that while they're much easier to use than the ones we tried a couple of years ago, they're imperfect replacements for conventional voice-call service. (link)