You will need a phone number, but you can make it work without a phone. signal-cli lets you register from a computer. If you have a modem in your computer, you

You will need a phone number, but you can make it work without a phone. signal-cli lets you register from a computer. If you have a modem in your computer, you can use this to receive the confirmation SMS. A friend also managed to register a landline (I think the phone received a code through a voice message).