In Gadgets Weblog you can find this post called Cell Phones = Sex…Who Knew?, that links to a studie from the Japonese Assiciation for Sex Education, where they find out that those who send 20 or more SMS/Emails per day from the cell phone have more sex than those who are hours in the internet.
They go even further. 80% of the students who send 20 or more SMS/Emails from the cell phone have sex, and only 20% of those who stay at home in the internet do it.