I received a message on the iPad the other day, and replied semi automatically. It didn't ever occur to me until a couple of hours later to wonder how on earth this had worked as there is no mobile phone functionality on an iPad.
I turns out that on iO6 there's an app called iMessages that sends texts over Wi-Fi rather than SMS to anyone with an iPhone, iPad or iPod touch.
I guess that Alex's mum was sending me a message from home so it went from her Wi-Fi to mine via the interwebs by default bypassing SMS altogether but blindsiding me.
All in all it is quite humbling never even to have heard of this when I mess about with devices for a living. I have no recollection whatsoever of setting it up for example.