It's been around for a while (SN post about release in September 2022 #73002), but I hadn't heard about it recently until I saw Blitz wallet saying they had some integration with it.
From their FAQs, there is this question
I used a number on sms4sats to sign up to a service but did not activate other forms of 2FA and communication methods. Service is asking me to validate the phone number again. What can I do? Unfortunately, it is currently not possible to recall numbers that were previously used. This is a limitation due to our providers. We are working on ways to make this possible in the future.
which seems like a problem.