The New York Times online edition's Personal Tech page published an article you might be interested in: "They're old enough to text. Now what?" The article is written by John Biggs, and was published: 26 August 2009.
Mr. Biggs describes how "children today have a plethora of high-tech gadgets they can use to phone and — more commonly — text with one another. The question most parents have is what type of texting gadget is appropriate for which age group." He gives some interesting parental viewpoints, and profiles example devices and plans a family might consider. Though the story is from the USA, the issues involved are universal.