At least in the US, you can still do the email-to-sms trick. In fact, I think that's exactly why so many sites ask who your carrier is (so they know which domain to use). Sending raw SMS, your carrier shouldn't matter.

http://www.att.com/esupport/article.jsp?sid=KB63037&cv=820#f...

http://support.t-mobile.com/docs/DOC-3309

http://www.verizonwireless.com/news/article/2013/06/computer...