If your contacts do not have an email address, you will not be able to assign them to a campaign, but you will be able to send them resources.
You can add the prospects to your account if you have their phone numbers.
However, you're limited to only sending them individual resources via text.
You will need to have their email address in order to assign them to a campaign. Please note, that contacts have to confirm through the opt-in email before they can start receiving campaign emails from you.
Please also see: Why can't I text the campaign?