Actually, it's not TSTT directly...
From what I understand, they were using the international gateway, just as tntsms.com used to do, and the international gateway is/was Rogers, a name that should be familiar to anyone in Canada...anyway, it is Rogers who shut them out...they blocked smstt.com first, and then followed with tntsms.com...I even had my own personal page for sending text messages that used the same method these 2 sites used, namely, suibmitting the form to the Rogers website, which would then prompt you for the characters in the image before it actually sent the message. Well this was working out nicely for me even after tntsms.com got locked down, and I figured since I didn't advertise it to anyone and the traffic on it would be really minimal, I'd have a good thing going for a long time...but then all of a sudden, it stopped. I believe they blocked any messages destined for an 868 code that didn't originate from a cell phone...the reason I say that is because I can still send text messages using my cell to TT cells, so the international gateway still works, they're just filtering it...
Couple that with TSTT not providing access to the local gateway, and it means no more free text messages...
