I get spam ad messages from a few companies regularly on my phone. And when I try to block them using the option given on the messaging application a custom message says that the number is invalid and cannot be blocked. So, how to stop such messages sent by unknown numbers?
Try this SMS Organizer app.
Apart from a host of other features, this app lets you set 'rules'. For example, you can set a rule to auto delete any message when the sender's phone number/contact name contains a certain sequence.
If you are unsure about deleting, you can also set the rule to move the sms to a folder (This app also lets you create folders for sms), say a spam folder