Hi! I'm off to the states for a week and need to send/received about 10-20 text messages and 5$ for 100 text msgs sounds perfect. There's not much information on how it works, can someone just confirm to me; - 100 incoming text messages = 5$ - Starts automatically and bills the 5$ as soon as msg 1 is received - 100 messages during my billing period? Or what? Thanks!!