How old does your child need to be to have a cell phone, how about a PDA, a portable laptop to do with a port-a-potty? It is an interesting question but I'm not too sure there is an exact answer. I just started letting my children borrow my cell phone a few months ago. AND you'd be surprised how old they are. Yes they have a laptop and use the Internet. But isn't technology supposed to be used to enhance our lives, supplementing and improving where needed? Maybe we could start a line of toys that would improve eye-thumb-finger coordination for instant messaging.
It is an interesting question and if you think you need help in this area, check out the aritcle: They gotta crawl before they can call