8 years old.
Expected to drop to 5 years old some time in 2006 or 2007.
http://crave.cnet.co.uk/mobiles/0,39...9282815,00.htm
We had neighbors in Houston whose little girls (pre-teens) talk on their cellphones all night long. I had to make our house a cell-phone free zone for them or they would talk on it constantly.
I don't have a problem with a kid of any age having one as long as they show discipline with them. When our niece comes over, I block her websites at the router because she's not disciplined enough to stay off of them. We'd come down in the morning and she'd have chatted all night if she could.
Anyhoo... I really look forward to the debates I'll have with the young'uns when they get just a few years older.