If this is something that the phone manufactuer is doing, there isn't really anything you can do about it except to not use their products. This sounds to me as if it could possibly be a device "phoning home" for whatever reason, and could possibly be some attempt to collect some basic information about you.
It's also possible for an app to send text messages without telling you.
This isn't specific to iPhone devices, but I do remember Nokia also did something similarly sneaky. Back in the days of Symbian 3, the Nokia N8 would send some type of short code text message back to Nokia after any factory reset. This was done without notifiying the user and it was never explained to customers what exactly Nokia was up to. The problem was that if a user did not have text messaging included in the cellular price plan, you would end up being charged for the message. Back then, I was with Wind, and because the shortcode wasn't considered a Canadian phone number, Wind would then proceed to charge extra for an international text message.
I know there's no way Public Mobile could charge extra for something like this, but in my opinion, phone manufactuers sending out texts automatically upon setting up the device is playing dirty. Who really knows what they are really up to.
