SMS needs an origination identity the way email needs a verified domain. Start with the sandbox sender: it works immediately but only delivers to verified test numbers (a carrier rule for unverified senders). A dedicated toll-free number unlocks production sending to any US number after a one-time verification.

A sender moves through registration and verification states before it's active, and its status is re-checked at send time — a suspended or released number can't silently keep sending. Number rental is billed to your card as a recurring line item, never drawn from your usage wallet.