Everything worth knowing, nothing that isn't.
The consent standard is not one standard
TCPA distinguishes between informational and marketing messages. Informational or transactional texts to an existing customer generally need prior express consent — the person gave you the number for that purpose. Marketing messages need prior express written consent: a clear disclosure that the person agrees to receive marketing texts, that consent is not a condition of purchase, and a record of when and how they agreed. A phone number collected for delivery notifications does not carry marketing consent.
Opt-out is immediate and permanent
STOP, UNSUBSCRIBE, CANCEL, END and QUIT must all be honoured, and the suppression must apply across the programme the person opted out of. One confirmation message after an opt-out is accepted practice; anything further is not. Re-adding a suppressed number requires fresh consent, not a new campaign.
Time windows and quiet hours
Messages may not be sent before 8am or after 9pm in the recipient's local time zone — which is the recipient's, not yours, and not the number's area code if they have moved. Programmes sending nationally have to schedule against a timezone map rather than a single send time, and a campaign that starts at 8am Eastern is already an hour early on the West Coast if you get this wrong.
How this interacts with 10DLC
TCPA is the law; 10DLC is the carrier registration regime that operates alongside it. Registering a brand and campaign with The Campaign Registry does not grant consent and does not discharge a TCPA obligation — it establishes who you are and what you intend to send so carriers will accept the traffic. You need both, and passing one does not imply the other.