Yes, you can send SMS in Salesforce using free SMS APIs with REST API callouts, but there are some important considerations.

How it works:

• Create a Named Credential in Salesforce to securely store the API endpoint and authentication.
• Use an Apex class with HttpRequest and HttpResponse to make the REST callout to the SMS provider’s API.
• Trigger this Apex via a Flow, Process Builder, or directly from custom buttons/Lightning components.

Things to watch out for:

• Many “free” SMS APIs are limited (low daily quota, branding in the message, or no delivery receipts).
• Be mindful of compliance – especially opt-in/opt-out rules and TCPA/GDPR requirements.
• Some free APIs don’t guarantee delivery, which can be risky for production use.

If you just want to experiment, you could try Twilio’s free trial credits or similar providers to build your prototype. But for long-term use, Salesforce-native apps from the AppExchange (like Message Blink) make this a lot easier – they handle bulk messaging, compliance, opt-in/out, and reporting inside Salesforce without you having to manage all the API plumbing yourself.