Most online casinos nowadays are mobile-friendly, which means that players can sign up and play on any device they like. Many casinos do not differentiate between players who sign up via desktop and those who sign up via mobile, so if a no-deposit bonus is offered, you will receive it no matter which method you use.
Casinos can choose to offer a different no deposit bonus for mobile users and you should reads the bonus terms and conditions to find out if this is right for you.