Stock spammers, even more than other spammers, go to considerable lengths to get the message out. I've written about some of the attachment formats that they use, and about their use of alternative media such as fax, but that's not the end of the options open to them by any means.
One of our contacts at a national regulatory agency is looking at SMS stock spam. If you've received any SMS messages advertising stocks, please tell us about it. At a minimum, say which symbols were advertised. If you can give the date(s), or the text of the message, or any other information that you think might be useful, that would be even better. I will pass any messages that I receive on to our contact, but I won't share your name or email address unless you specifically tell me that it's OK to do so. Thanks in advance!