I really didn't have much choice. My stepdaughter kept breaking her phones and I had to constantly use my wife's and my upgrades to get her new phones once the phone insurance wouldn't give us anymore. I swear that kid has gone through at least 7 phones to my 1.
She's on her 3rd iPhone 4s and now that she will be 18 this year, I let her know that will be her very last phone on my plan. Once that phone breaks she will have to go out and get her own plan. (knowing my luck she will make that phone last forever now though)
I had a motorola Razr flip phone before my Droid. That darn thing also lasted forever, in fact I still have in a drawer and it still looks and works like new if I were to charge it. I always like to keep a few spares around in case one of our phones do break and we need a temp. one.
You are an awesome parent. My daughter would be getting a cheapy little flippy phone if she broke one $700 phone never mind three. She did actually fry her Samsung Gio by giving it a bath in her water glass beside her bed....I got the new phone, she got the old one. I also warned her if she kills that one she better get a job to pay for a new one.