If you don't have a dedicated short code, the other carrier-approved option is an A2P 10DLC number. A registered long code helps mitigate spam and slow throughput issues, which often occur because carriers are blocking mass texts from P2P numbers (long codes that aren't registered). When you send a text to a friend or your Uber driver lets you know they've arrived — those are P2P exchanges. When you text a small group or inform your church about service changes — those are A2P exchanges.