Don't know if it costs to text the number! but might work out cheaper than paying for the 1gb itself? I'm on contract so I assume it's contracts only?
Also I was sat next to my friend when I got the text and we're both on vodafone, But she still hasn't received it! Yet she still did it without the text (messaged data to 97888) and got the 1gb free data! So give it a try :)