Blocking Calls from a Specific Number:

1. Press the "Menu" button while on a home screen
2. Tap "System settings"
3. Tap "Call" > "Call reject"
4. If necessary, tap "Call reject mode" > "Reject calls on list", and skip the next step
5. Tap "Rejection list"
6. Press the "Add" button and select one of the following:
   
   • To block a contact: select the contact and tap "Done"
   • To block a number from the call log: select the desired call log entry and tap "Done"
   • To block a phone number: enter the phone number and tap "Save"

Unblocking a Contact / Phone Number:

1. From any of the home screens, press the "Menu" button
2. Tap "System settings"
3. Tap "Call" > "Call reject"
4. Tap "Rejection list" and touch the icon depicting a trash can
5. Choose the phone numbers that you wish to unblock
6. Tap "Delete" and press "Yes" to confirm

Blocking Calls Using Applications:

If you feel like the call barring options offered by the LG L90 are not meeting your requirements, then you can try using various third party applications to block phone calls. There are apps such as "Call Blocker", "Call Blacklist" and "Call Control" (or similar apps), which offer a wide range of blocking options, including the ability to block messages, and password protect the blocking app.