Using an application or a third-party service blocks unwanted calls to a cellphone. Some cellphones include phone book blocking features that can be used to block certain calls.
Native phone book blocking allows a user to block calls from a number on his contact list. To block a number from the list select the Menu key or button.
Choose Phone Settings or Settings and Phone; then select Calls or Incoming Calls. When a menu option such as Unwanted Calls, Blacklist or Blocked Callers appears, choose the applicable option and the phone book or contact list appears on screen.
Choose the name of the person whose calls you want to block. Choose Block or OK. To block calls from someone whose name is not in the contact list, enter the phone number in the number field, then select Block or OK.
Exit the cellphone's menu screen. Future calls from the blocked number should no longer appear on screen or make the cellphone ring. The blocked caller hears either a busy tone or a message stating the cellphone doesn't accept calls from that number.
Some wireless carriers offering call blocking may charge customers for stopping incoming calls. Android users can send calls from numbers in the contact list directly to voicemail. Apple iPhone users must "jailbreak" the phone before using this feature. Jailbreaking an iPhone violates the warranty.