Ok so for a typical IoT device I have the software on the device that talks to some server/service on the Internet, and an app on my phone to control the device

Ok so for a typical IoT device I have the software on the device that talks to some server/service on the Internet, and an app on my phone to control the device. This replaces the server/service? What about the app? Does that mean I can create my own devices and an Amazon Echo or Siri will eventually be able to talk to it?