A visitor can subscribe to to text updates by providing their phone number
The full functionality for this will be more difficult than e-mail (and need to confirm if Twilio or another provider is broadly effective for all Nigerian and other African and beyond cell service carriers) and possibly not cost-effective; sending out texts costs more money than sending out e-mails. But it is important to establish if it is possible to establish a direct relationship with readers outside of search engines and social media, and see if these readers can become donors, promoters, etc that makes the cost of sending worthwhile.
And again, we can simply start with a form that indicates text notifications of news stories is a service that SaharaReporters.com is thinking of starting, and maybe provide some options for which types of stories (breaking news only? politics? entertainment?) people can subscribe to notifications to.