Vodacom has implemented a CAPTCHA on their SMS forms on vodacom.co.za.
The CAPTCHA (distorted 'polthed' text in the above image) is intended to make it difficult for 3rd party robots to send free SMS from vodacom.co.za. Websites that will be affected by this CAPTCHA include popular free SMS robot sites Free082SMS.co.za and defza.com. However, Free082SMS does offer several alternative options for free SMS in South Africa.
Otherwise Vodacom users are now forced to login to the desktop version of vodacom.co.za directly to access their ration of 20 free Vodacom SMS per day. I'm sure that Vodacom is hoping that this move will encourage Vodacom users to make increased use of the Vodacom website and get more involved in the new Vodacom Community.
Update: It is possible to access your 20 free SMS from the My Vodacom App on smartphones and it is also possible to login to the desktop version of the Vodacom website from certain phones - more info here.