If you send a message that happens to go to a friend on another network today, it will go through my software.

Inter-Carrier text messaging is one of those systems that are at their best when you have no idea they exist. Early on in mobile phones, text messaging only worked within a carrier. i.e., you could only send it to someone on the same carrier as you. Early advertisements tried to spin this as ‘you and your friend can join together, and you can send text messages.’ Of course, that spin didn’t last too long.

Today, I understand that over 10 billion messages a day flow through the inter-carrier system. (It started as 100,000 on the first day)

Carriers didn’t want to take on the interconnection work because it would have been daunting… getting agreements and doing software development with every other peer carrier. That route would have resulted in n times n agreements. Instead, they opted to have a third-party deal with the interconnection.

MobileSpring (Eventually acquired by RealNetworks) developed a product where it took in the ‘destination phone not on my network’ traffic from a carrier and routed it to other carriers (and eventually to another ‘inter-carrier’ company that by industry agreement, took on the other 50% of the countries inter-carrier traffic).

MobileSpring’s first customer was Sprint. Initially, since there were no other carriers, the message was converted into email (and vice versa).

Initially, the product worked from something called the LERG, which mapped the first six digits of a phone number to the carrier that owned those digits. Shortly after its introduction, ‘wireless number portability’ became law, and people could move their numbers from carrier to carrier. This made it so we had to query a central number authority for every message.