Cell phone wrecks sleep, maybe

The Independent (UK) has a story running under the title "Mobile phone radiation wrecks your sleep." They write:

A massive study, following 1,656 Belgian teenagers for a year, found most of them used their phones after going to bed. It concluded that those who did this once a week were more than three times – and those who used them more often more than five times – as likely to be "very tired".

If we accept the Independent's description of the study at face value, this only says that frequently carrying on conversations after going to bed leads to being "very tired." To identify the cause as cell phone usage, the researchers needed to compare those who talk too much by wired phone to those who talk too much by wireless (cell) phone.