William Dudley DeMystifying Messaging Series, MMS, RCS, SMS

Demystifying the US Messaging Ecosystem: Part 2: Understanding A2P and P2P Messaging: A Deep Dive into the Messaging Matrix

This post is the second installment in our Demystifying the US Messaging Ecosystem series. Having provided a macro-level overview in our first post, we will now look at the fundamental distinction that governs the entire landscape: the difference between Application-to-Person (A2P) and Person-to-Person (P2P) messaging. While often viewed as similar on the surface, their underlying technologies, use cases, and regulatory frameworks are vastly different, shaping how we communicate in a digital world.

The Core Distinction: A Tale of Two Messaging Types

At a high level, the messaging world is a clear-cut dichotomy between P2P and A2P. The P2P (Person-to-Person) channel is a free and open communication tool, facilitating conversations between individual consumers. Conversely, A2P (Application-to-Person) is a commercial service, a highly regulated and controlled channel for businesses to communicate with consumers. The core difference lies not in the message itself, but in the originator and the intent of the communication.

The CTIA’s Messaging Principles and Best Practices provide the definitive framework for this classification. While the most recent CTIA documents have updated the terminology to “Consumer” and “Non-Consumer” messaging, the industry continues to widely use the legacy P2P and A2P terms.

According to the CTIA, P2P (or Consumer messaging) is defined by these core characteristics:

  • Originator: The message sender is an individual consumer who sends messages to one or more other consumers.
  • Purpose: The messages are personal in nature, intended for direct, one-on-one, or group communication.
  • Conversational Flow: P2P traffic is typically conversational, with an expected back-and-forth exchange between parties.

To enforce this distinction and identify traffic that is not genuinely P2P, carriers and messaging aggregators look “under the covers” at a message’s behavioral attributes. P2P traffic is characterized by a “typical human operation” pattern, and traffic that deviates from this can be flagged as unauthorized A2P. The CTIA Guidelines define specific metrics that are used by carriers and aggregators to differentiate legitimate P2P traffic from unauthorized A2P messages that are trying to masquerade as personal conversations. They are also used in various volumetric filter combinations to catch spammers and unwanted messaging.

The key metrics and characteristics that define P2P messaging are:

  • Throughput: The number of messages sent per phone number per minute. A P2P user is typically expected to send no more than 15 to 60 messages per minute. Sending messages faster than this can be a sign of automation.
  • Volume: The total number of messages sent per phone number over a day. P2P traffic generally stays below a few hundred messages, with a guideline of no more than 1,000 messages per day as a common threshold.
  • Balance: The ratio of outgoing messages to incoming messages. A P2P conversation is conversational, so it’s expected to have a roughly 1:1 ratio of outgoing to incoming messages. An extremely high number of outgoing messages with no replies is a red flag for spam.
  • Repetition: P2P messages are not repetitive. Sending more than 25 repetitive messages is considered an A2P characteristic.
  • Unique Recipients: The number of distinct recipients a single phone number texts. P2P traffic is typically sent to a limited number of recipients (e.g., a few close friends), with a guideline of no more than 100 unique recipients per message.

The CTIA emphasizes that these are guidelines, and a single metric violation may not get a message blocked. However, when a message’s behavior exhibits multiple red flags across these metrics, it significantly increases the risk of being filtered or blocked by carriers as “unwanted messaging traffic.” Both carriers and inter-carrier aggregators use these metrics in various volumetric filters to make sure P2P messages are not overwhelming subscribers with spam.  And I can attest that these actually work very well, having managed SMS/MMS spam control for many years.

The P2P Ecosystem: Where Security and Convenience Collide

The P2P ecosystem is not monolithic. It includes traditional carrier-to-carrier SMS and the rapidly growing volume of Rich Communication Services (RCS) traffic. This classification also applies to messages from popular SMS-enabled Over-the-Top (OTT) messaging services like Pinger’s TextFree, TextNow, TextMe and many others, as their core purpose is to facilitate personal communication, even if they ride over data networks.

The ongoing shift of P2P traffic from SMS to RCS has brought with it a new set of challenges and opportunities. On one hand, RCS offers a richer, more engaging experience. On the other, it creates new attack vectors for spammers, who are attempting to exploit the channel’s open nature.  But defenders are also getting ready too. For more information about P2P RCS spam control, refer to my deep dive: Demystifying the Digital Inbox: How RCS P2P Spam Control Works.

A2P: The Engine of Commerce and Accountability

A2P messaging is the ecosystem’s engine for business communication. It is a commercial activity governed by strict rules and best practices designed to protect consumers from unwanted spam and fraud. The US A2P ecosystem relies on three primary messaging channels.

  • 10DLC (10-Digit Long Code): This channel is defined by its use of a standard 10-digit number for A2P traffic.
  • Short Codes: These five or six-digit numbers are the traditional backbone of high-volume A2P messaging.
  • Toll-Free Texting: This channel uses existing toll-free numbers (e.g., 800, 888) to send and receive text messages.

The Central Role of The Campaign Registry (TCR)

For the 10DLC ecosystem, the largest A2P channel with over 2.8 million campaigns as of September 2025,  to thrive, a centralized authority was needed to enforce accountability and prevent abuse. This is the purpose of The Campaign Registry (TCR). TCR serves as the sole source of truth for all A2P messaging campaigns that use 10-digit Long Codes (10DLC) as sender IDs. Its primary functions are:

  1. Brand Vetting: TCR vets and registers every brand that intends to send 10DLC messages. This ensures that the message sender is a legitimate entity, building trust from the very start.  TCR does not vet individual campaigns. That is done by the various DCAs that act as gatekeepers through their connections to the MNOs.
  2. Campaign Registration: Each specific messaging use case—be it a marketing campaign, a security alert system, or a two-factor authentication service—must be registered within TCR. Once registered, TCR can facilitate DCA campaign vetting. This provides transparency to the carriers, giving them clear visibility into the type of traffic on their networks.
  3. Coordination of Communications: TCR’s portal, APIs, regular carrier communications, shared knowledge base, and close coordination with CSPs/DCA help the entire 10DLC ecosystem be more effective and run smoothly.  And that becomes a very high value benefit that creates a lot of transparency regarding how campaigns will be managed (and pinpoint communication when there is a problem) which enables the overall channel to be highly efficient.

The scale of TCR’s work is impressive and points to the massive potential for continued growth. According to recent data, there are at least 2.8 million active 10DLC campaigns from over 4 million registered brands. This significant gap between registered brands and active campaigns indicates that there is still substantial additional growth to come in the A2P 10DLC marketplace, even as RBM (Rich Business Messaging) takes on significance in this marketplace.

The Role of Aggregators and The UCaaS Gray Area

The messaging ecosystem is highly reliant on key aggregators like Sinch, Syniverse, ClearSky, and Interop Technologies. These companies act as vital bridges, providing a single connection for brands to access messaging channels across a wide array of carriers, including smaller and regional carriers (like those that are part of the Competitive Carriers Association, or CCA) and OTT providers. For instance, recent partnerships, such as ClearSky’s agreement with Vibes, are enabling RCS for Business campaigns to flow from enterprise clients to regional carriers, opening new revenue streams and ensuring that no part of the network is left behind.

A key point of differentiation in the A2P world is the classification of Unified Communications as a Service (UCaaS) traffic. While a UCaaS user may send a personal message from their business phone number, the carriers have a clear preference for how this traffic is classified. UCaaS traffic, by its very nature, is A2P. The message is being sent from a number provisioned to an application (the UCaaS platform) as part of a business’s communication workflow. Carriers require that UCaaS traffic be registered and compliant with A2P rules, and The Campaign Registry even has a specific “UCaaS” campaign type to ensure visibility and accountability. This has certainly been a topic of debate and discussion, but that continues to be position of carriers and DCAs as well. 

A Framework of Standards and Best Practices

The integrity of the entire A2P ecosystem is upheld by a comprehensive framework of regulations, standards, and best practices.

  • TCPA (Telephone Consumer Protection Act): This federal law is the most important legal standard. It mandates that businesses must obtain prior express consent from consumers before sending them non-informational text messages. Recent FCC changes in 2025 have further tightened these rules, mandating one-to-one consent for marketing messages; however, this tightening and other TCPA regulations may also be lessening  as well.  For more information, refer to my page: Navigating the Evolving TCPA Landscape: What you Need to Know for 2025 and Beyond.
  • CTIA (Cellular Telecommunications Industry Association): The CTIA provides key support for A2P or Business Messaging in the Messaging Principles and Best Practices. These guidelines on consent, opt-out, and content are highly influential and are the basis for carriers’ own Codes of Conduct.  Of course, as we noted earlier, the definition of Consumer-to-Consumer texting (or P2P) is also specifically set out in this document.
  • Carrier Codes of Conduct: Each major carrier (AT&T, Verizon, T-Mobile) has its own specific Code of Conduct. While they generally align with CTIA principles, they may have additional rules related to content, volume, and acceptable use, which are essential for A2P senders to follow.

In summary, the distinction between P2P and A2P messaging is not just about the sender, but about the technology, regulations, and trust required to operate in each space. As the P2P world shifts from SMS to a more secure RCS, the A2P ecosystem continues to mature and professionalize, providing a reliable and compliant channel for business communication.

Looking Ahead

The next post (2nd half of September) will be a deep dive into The Campaign Registry (TCR), itself – one of the most important stakeholders in the huge 10DLC ecosystem. We will go deeper into its function as the reputation authority for 10DLC messaging, detailing the brand and campaign registration process and its critical role in ensuring message deliverability and trust within the ecosystem, all within the framework of CTIA Guidelines.