Toktumi's Line2 Professional app is a second line for your iPhone. It lets you make calls using Wi-Fi or 3G service instead of your cellular network. The app, a follow-up to Toktumi's popular Line2 software, gives your phone a second number and separate calling interface. You can use the app to place and receive calls over Wi-Fi or 3G whenever service is available. The app also lets you text during airplane flights using Wi-Fi. We tested it on a flight from Minneapolis to Detroit and had no trouble sending and receiving texts. On the return trip, however, the Wi-Fi connection was spotty, and some messages did not go through. Cost: $15 a month.