A2P 10DLC stands for Application to Person messaging, which refers to SMS traffic sent from an application to a person rather than another individual. It was created due to the increase in spam messages on 10-digit long code numbers in the US, which were originally designed for Person-to-Person communication. The A2P 10DLC registration process is necessary for individuals sending SMS messages to people in the US, as carriers filter or block unregistered and verified messages. Individuals can use Toll-Free or shortcode numbers instead of 10DLC numbers, but may need to register for an EIN with the IRS to use certain messaging options. The registration process will become available through Twilio in early 2023.