SMSMeOn allows you to register a keyword on their SMS Short Code 56070 for free.
You start by searching for an available keyword (labnol, for example), and associating a mobile phone number to it. SMSMeOn then sends you your login details via SMS, which can be used to login to the web interface. You can now set updates either directly via SMS or the web interface.
To subscribe to the updates, simply SMS “labnol” to 56070. (Thanks AlooTechie)