The third part of a five-part series discusses the differences between three types of Application-to-Person (A2P) messaging - short codes, toll-free numbers, and local 10-digit numbers (10DLC). While short codes were once the only way to send high-volume A2P messages, technology has evolved to allow toll-free and local numbers to deliver A2P messages at scale. The right type of A2P messaging depends on factors such as message volume, number cost, time to market, and user experience. Short codes are best for 'text-in' campaigns, while toll-free and local numbers may be more suitable for other types of messaging.