Hi Rajj, Unfortunately, there is currently no native implementation of a call block or blacklist in Firefox OS. It is currently on backlog for implementation in future versions of Firefox OS, and can be tracked in the [https://bugzilla.mozilla.org/show_bug.cgi?id=970827 bugzilla ticket #970827]. In the meantime, your carrier may be able to provide a way of blocking calls through a sequence of numbers or codes in your phone. I hope this information is helpful. Please let us know if your problem is resolved, or if you have any other questions. Thanks, - Ralph