Seems like a good idea in my opinion but pjc has a point in not sure of the ratio in our club but i would say its likely 40% of the membership dont have mobile phones.
Another thing from looking is that it costs 10p per text, which is fair enough but on my mobile phone i can basically do the same as the service offered by setting up a group in my phone contact list and then send a multiple message to all members of that group which would take as long to do as the service offered by the website.
The post may sound like its knocking the service but i will keep an eye on it as more clubs become involved.
Best wishes the idea.