I've noticed a lot of occasions where a child (usually between say 10 and 16) has committed some misdemeanour, and is to be punished. So often though I hear "oh I can't take away DS/DD's phone, they need it for emergencies."
What sort of emergency does a 15 year old need a phone for all the time? For a true emergency (fire, car accident etc) there are phone boxes (there's still plenty around), and I'm sure nobody would object to someone borrowing their mobile phone to call an ambulance.
Mobile phones make life more convenient I'll admit - it saves you coming home first if you want to pop round to your friend's house etc, but surely part of the punishment of having your phone taken away should be curtailment of the lifestyle it enhances?
My kids aren't old enough to (allegedly) need phones, but from a personal point of view if I leave my phone at home when I go to work, it just means I have to keep my commitments, and make a phone call using a land line if I have to change anything important.
I can't believe how old I feel writing this, but I never had a mobile phone until I was 17 (30 now) and I feel like kids are in more danger from having mobiles (exposure to unsolicited texts, photos, bullying) than I ever was from NOT having a phone.