The ability to block a number from calling a mobile device varies by service provider. For example, both Verizon and AT&T offer services that temporarily block certain callers from calling a specific mobile number. Some cell phones also offer settings to block individual callers.
AT&T offers a program called Smart Limits, allowing someone to block unwanted calls and texts from up to 30 different numbers. This only works for inbound calls from known numbers, not from anonymous callers. As of 2014, this feature costs $4.99 per month. Verizon offers a service on its website allowing mobile customers to sign up for a free Block Calls & Messages service. It can block up to five phone numbers per line for 90 days.
Some phones have the capability of blocking individual callers as well. For example, Samsung phones can block specific callers if a user goes to the Contacts menu, chooses Logs or Contacts, and selects users to "Add to Blacklist." Apple iPhones with iOS 7 or later can also block callers by going to the Phone app, going to Favorites, Recents, or Contacts, tapping the info button of the name or number to block, scrolling to the bottom, and tapping Block This Caller, then tapping Block Contact.