my teenager is going on school tour trip next week for 13 days.from U.S. to Germany,Prague,Paris & the Alps. they are not allowed to bring any electronics.i want her to be able to call me if she wants to.i have no idea what is the easiest way to do so. payphones? prepaid phone cards? prepaid phones? disposable phones? whats best? which country to buy from? where to find them to buy? how much cost? any additional costs? etc. HELP PLEASE ASAP thank you signed-mother of only child!