This would be problematic e.g. in the case of ported numbers, or if a customer is using a third party to send their SMS for a fraction of the cost. Implementing

This would be problematic e.g. in the case of ported numbers, or if a customer is using a third party to send their SMS for a fraction of the cost. Implementing such blocks without covering these use cases would likely (rightfully) result in antitrust issues.