How does a text message get to the other phone?

We put this question to Professor Mark Beach, Bristol University...

Mark - The characters that you type into the phone get sent as a data message back to the cell site and attached to that is the mobile phone number of the person you wish to send it to, so that's routed through the network and the message is dispatched to that phone.

Dave - I heard somewhere that text messages were just put into a bit of spare space which they have in the way that they designed their system, and that was put in as an afterthought very, very late on design.

Mark - It wasn't actually putting it as an afterthought. The original concept behind the short message service was to help the engineers who were effectively rolling out the network, putting the base stations up and adjusting all the parameters that make the network tick. So this is a way for them to report back how well it was working and they suddenly repurposed that for the commercial service that we have today for texting.