I Did an interview for CIO East Africa (www.cio.co.ke) with Gichuki Jonia and Evans Kahuthu who are security consultants. Part of the interviews, they talk about how individuals leave their telephone numbers and details in several 'visitors books' and how individuals are harvesting this information to create databases.
Its the high time you became careful with where you leave your details. Even in campus, they have databses for students which are sold to those vying for student body elections.
Be careful of where you leave your details, it is the high time you stopped jotting your ID number and phone number on books that watchmen can hire at a small fee.