MMS (Multimedia Messaging Service) is the 3GPP multimedia companion to SMS. The original architecture is specified in 3GPP TS 23.140 (MMS stage 2) and related specs; later deployments ride IMS. Unlike SMS, which is a 140-byte signaling payload, MMS stores a multimedia object on an MMSC (Multimedia Messaging Service Center) and sends the handset a notification (often an SMS) to retrieve it over IP.
That retrieval step is why MMS can carry a photo and why it fails on a handset with no data path, a blocked MMSC hostname, or a roaming profile that does not allow MMS. Group messaging on many US Android and iPhone threads is MMS (or, when both sides support it, RCS), not concatenated SMS.
Size limits vary by carrier
There is no single ITU or CTIA maximum MMS size that every US operator implements. Each wireless carrier (and sometimes each MMSC vendor) sets a cap. Values commonly seen in US A2P interconnect in the 2020s range from a few hundred kilobytes to around one to one and a half megabytes. Oversize content is resized, rejected, or transcoded into a poorer image. Video is more often rejected than still images. What leaves a CPaaS API as “one MMS” may be transcoded several times before it reaches the handset.
| Topic | SMS | MMS | Practical consequence |
|---|---|---|---|
| Spec family | 3GPP TS 23.040 / GSM 03.40 PDUs | 3GPP TS 23.140 and successor IMS MMS | Different centers (SMSC vs MMSC), different failure modes. |
| Payload | 140 bytes per segment | A multimedia message whose cap is set by the terminating carrier / MMSC | Do not assume a 1 MB image will land on every US MNO. |
| Group conversations | Poor fit (fan-out of many 1:1 SMS) | Native group MMS on many handsets | A2P group send is still A2P; it needs the same 10DLC or other registration as 1:1. |
| Throughput accounting | Segments | Often a separate, lower MMS TPM or a heavier segment weight | AT&T 10DLC message class tables quote SMS TPM and MMS TPM separately. |
| Fallback | N/A | Some paths fall back to SMS with a link if MMS cannot be delivered | The recipient then sees a URL, not the media. That is still A2P content. |
Content, transcoding, and compliance
- Supported objects in practice: JPEG/PNG images, short video in a carrier-accepted codec, AMR or AAC audio, vCard, sometimes SMIL layout.
- A2P MMS on a US long code still requires 10DLC campaign association. On 8XX it still requires Toll-free texting verification. SHAFT and TCPA rules do not disappear because the payload is a picture.
- RCS can replace MMS for rich media when both clients and both networks support it. Where they do not, MMS remains the interoperable multimedia path.