When SMS first exploded in popularity back in the day a friend of mine worked at BT (British Telecom) and pointed out that the entire network's SMS traffic was

When SMS first exploded in popularity back in the day a friend of mine worked at BT (British Telecom) and pointed out that the entire network's SMS traffic was handled by 3 mid-range sun sparc servers. Since SMS was originally designed to use management channels it was already built into the general infrastructure, they just needed to up the server count to 3. SMS was (and maybe still is?) almost pure profit for at least BT and I imagine other carriers.