What's wrong with it is that it only applies to messages sent between 021 phones. When Telecom released $10 text back in 2003, the kids all bought 027 handsets as soon as they could save up enough pocket money. By the time Vodafone had released free text weekends, Telecom's market share in that demographic had grown to the point where disqualifying 027-bound messages from free text weekends was considered to be a major drawback.

In any case, I personally think that $10 text and free text weekends are both overrated. The only time I ever use text messaging these days is if I want to communicate with someone when the environment is too noisy to make a phone call (e.g. a bar). People seem to use text messaging because of the perception that it's cheaper, but if you consider how much information you could communicate during a one minute phone call versus the information that you can communicate in one text message, then you have to wonder if it's worth the hassle of awkwardly typing out silly little messages on a cramped telephone keypad.