Servers are owned by whoever wants to run one. And they're located all over. Many individuals and organizations are running SMP (message) servers, and you can setup your own in literally under a minute. It's the basis for the decentralized, distributed architecture.
Discussion
where can I order a server please?
If you'd like to run your own server, or just look at the code for the SMP server, you can find what you need on SimpleX Chat's GitHub. Here's a link to the latest server software:
👉 https://github.com/simplex-chat/simplexmq/releases/tag/v6.0.3