How do SMS and call forwarding services work?

Question

SMS

Good evening.

There are many services for receiving SMS online.
An example of simsms org, etc.

There is a desire at home to raise such a service in order to receive SMS and set up call forwarding for each number to the main "own" number. How can this be implemented? What do you need to buy? I looked at a lot of resources, https://www.youtube.com/watch?v=SVHYlNUkZ4E , all sorts of GSM gateways, but there it is purely to receive SMS. Please advise