SMS Opt-In Proof
Trestle Social phone signup and SMS consent screen.

The SMS consent checkbox is unchecked by default. The user must affirmatively select it. It is not pre-checked, not required to create an account, and not bundled with any other agreement. Consent to SMS is separate from acceptance of the Terms of Service and Privacy Policy.
The agreements linked from the signup screen above are reachable here as real links: