Lam Bui Quang, Apologies the delayed response. I'd been discussing on this internally for any other alternative options.
Yes, as outlined in the doc 'Send SMS' feature is currently not available for Singapore. You may need to signup on the supported region for this feature.
Additionally, *applications from all other subscription types are reviewed and approved on a case-by-case basis. Reach out to acstns(at)microsoft(dot)com for assistance with your application.
Kindly be assured that I have relayed this feedback internally to our product team.
If you wish you may share your feedback on Uservoice - All of the feedback, you share in these forums will be monitored and reviewed by the Microsoft engineering teams responsible for building Azure. Additionally, users with a similar request can up-vote your post and add their comments.
ACS repo: https://github.com/Azure/Communication/issues
ACS Roadmap: https://github.com/Azure/Communication/blob/master/roadmap.md
As soon as I have any more updates on this, I'll share it here.
If the answer helped (pointed, you in the right direction) > please click Accept Answer - it will benefit the community to find the answers quickly.