A small South Carolina company says it has a cure for the modern plague of budget-busting cell phone charges racked up by teenagers: a gadget for text messaging that isn’t a cell phone. Zipit Wireless plans to announce Tuesday that it will make available a text-messaging plan for its Zipit Wireless Messenger 2, a device the size of fat wallet that uses WiFi hotspots to do free instant messaging with AOL Instant Messenger, Yahoo Messenger and Windows Live Messenger.