[hollosi]

SMS forwarding sends the content, not the sender (phone number) info. In principle, they can search your previous messages and find the sender, but it's unclear if that would raise some privacy issues.

Most likely they just use the reported message to train their spam filter, not to block the particular sender number of that message.

[ericbarrett]

You're probably right, but mining the results of that trained filter should provide quite a bit of data to a telco even so. It's not like it's a new bad actor for every message.