Skype is launching service for the iPhone tomorrow, expanding its popular internet phone operation from computers to the lucrative mobile market. Users of iPhones as well as iPod Touches—which have wifi but no cell connection—will be able to make free calls to fellow Skype users and pay for others. The company is planning a BlackBerry launch in May, Reuters reports. Skype is popular in Europe, but US carriers have been slow to adapt. Next up for Skype is making video calling mobile.