Until Twilio is connected, SMS runs in simulated mode: messages are recorded on the applicant record and in the inbox with a Simulated status, but nothing is delivered. This is how the free trial works, and it is a safe way to test templates.
US carrier registration (A2P 10DLC)
US carriers require businesses that text from local numbers to register their brand and campaign. Twilio walks you through this in their console and it usually takes a few business days. Until registration is approved, carriers may filter or block messages. Describe the campaign as recruiting and applicant communication, with opt-in collected on your careers page.
Consent
Only text applicants who consented. The apply form on your careers page includes a consent checkbox and stores the timestamp on the applicant record. If an applicant came from a CSV import or a job board, get consent by email or in your first phone call before texting.