We use Twilio as our SMS provider.
Merchants who have setup SMS Alerts will receive SMS Alert messages from different originating phone #s.
"In the United States, it’s typically recommended that you add one long code number for every 200 unique recipients per day (because long codes are intended for person-to-person traffic). For example, if your SMS technical support number typically exchanges messages with 1,000 people a day, you should add 5 phone numbers to your Messaging Service."
Ref: https://www.twilio.com/docs/sms/services/copilot-best-practices