For registering you need a phone number where you can receive SMS or incoming calls.
signal-cli is primarily intended to be used on servers to notify admins of important events. For this use-case, it has a dbus interface ([man page](https://github.com/AsamK/signal-cli/blob/master/man/signal-cli-dbus.5.adoc)), that can be used to send messages from any programming language that has dbus bindings.
For registering you need a phone number where you can receive SMS or incoming calls.
signal-cli is primarily intended to be used on servers to notify admins of important events. For this use-case, it has a dbus interface ([man page](https://github.com/AsamK/signal-cli/blob/master/man/signal-cli-dbus.5.adoc)), that can be used to send messages from any programming language that has dbus bindings.