Right before you enter any on-air related SMS contest, you have to register yourself (with your mobile phone) first. It's not that hard actually to do so, you just have to sms

JOIN <space>full name

and send it to

33399

and you'll get an acknowledgement SMS that you've successfully registered.
It's as simple as that.

If you had any difficulties understanding the paragraph above, follow the easy graphical steps below.

Yeap yeap, as easy as 1, 2, 3.
Now you're all set! Yay!