Well, I held off for as long as I could--Just got it last January, so I was 40! What finally made me break down and do it was the fact that there are no longer any pay phones anywhere! DH and I were carpooling and he has a tendency to lose track of time so I was sitting outside waiting and waiting for him. I can't get into his office because he works for the state and you have to get security clearance to get into his area. I ended up having to drive back to my office because I could not find a payphone.
I got one for DD at the same time on the family plan (she's 13). She also had a hard time calling me when she was out due to the same problem. She's been very responsible on it--only calling her friends on the weekends when it's free. I'm very proud of how good she's been with it. In fact, I had to tell her that she could call her dad (we're divorced) whenever she wanted on that phone--she told me, but Mom, I couldn't call him because it wasn't the weekend!