MySMSBlocker

MySMSBlocker is a simple app to mark messages as junk if they match various filters. Unlike other apps, this app does NOT send your data to a server for analysis; everything is local.
When a message comes in, iOS passes the message to MySMSBlocker and MySMSBlocker goes through your filter list to see if the message should be marked as Junk or not. If there are no matches, it is simply listed as from an Unknown Sender.
Filters are synced via iCloud.
The source for the app is freely available at https://github.com/sgruby/mysmsblocker.
Notes:
• This only filters SMS and not iMessages.
• If a sender is in your contacts, the filtering is not used.
• There is no equivalent app on the Mac, so it is recommended that you turn off notifications for Messages on your Mac if you sync your Messages across devices.