Well, buy you kids a prepaid phone - like the ones at Virgin Mobile. Buy the cheapest device, something for $20-25, with the basic functions like calls and text. Nothing fancy. The kids will learn to be responsible, to stay into their limits for the month.
Virgin offers prepaid cards for $20 and they are good for 90 days.
Of course you have to teach your kids that the phone is for emergency only. No trash talks for an hour or so.
I can tell you that my kids were OK with this until their senior year in college. Now they both have their degrees - one in Finance, the other is a Doctor. Now they have the best phones and plans in the world but when they were kids they have restrictions and they thank me for that.