If you use Gmail follow these steps:
1. On your BlackBerry device, navigate to your home screen
2. Select the icon that lets you set up email (this can be called Setup, Setup Wizard, Email Setup, BlackBerry Set-up, E-mail settings, or Personal Email Set-up)
3. Follow the setup instructions provided on your device
If setup is successful, you should receive a confirmation message and a new mailbox icon should appear on your device's home screen, labeled with your Gmail address.
If you encounter a problem during setup, please make sure you have enabled IMAP in your main Gmail settings.
I think these steps will also apply to Yahoo, Live and Hotmail.