Multimedia Messaging Service, or MMS, is a standard way to send messages that include multimedia content to and from cell / mobile phones. It extends the core SMS (Short Message Service) capability that allows the exchange of text messages (only) up to 160 characters in length.
The most popular use of MMS is to send photographs from camera-equipped handsets, although it is often used as a method to deliver news and entertainment content including videos, pictures, text pages and ringtones.
The MMS standard was developed by the Open Mobile Alliance (OMA), although during development it was part of the 3GPP and WAP groups.
The initial idea behind multimedia messaging services was to use them as a captive technology that would enable service providers to "collect a fee every time anyone snapped a photo."
The early use of MMS was plagued by technical issues resulting in frequent user disappointment, such as having sent an MMS message, receiving a confirmation it had been sent, being billed for the MMS message, only to find that it had not been delivered to the intended recipient. Pictures would often arrive in the wrong format, and other media elements might be removed such as a video clip arriving without its sound.
At the MMS World Congress in 2004 in Vienna, all European mobile operator representatives who had launched MMS, admitted their MMS services were not making money for their networks. Also, on all networks at the time, the most common uses were various adult oriented services that had been deployed using MMS.
China was one of the early markets to make MMS a major commercial success, partly as the penetration rate of personal computers was modest but MMS-capable cameraphones spread rapidly. The chairman and CEO of China Mobile said at the GSM Association Mobile Asia Congress in 2009 that MMS in China had become a mature service on par with SMS text messaging.
Europe's most advanced MMS market has been Norway, and in 2008 the Norwegian MMS usage level had passed 84% of all mobile / cell phone subscribers. Norwegian mobile subscribers send, on average, one MMS per week.
By 2008, worldwide MMS usage level had passed 1.3 billion active users, who generated 50 billion MMS messages, and produced annual revenues of 26 billion dollars for mobile phone companies.
MMS messages are delivered in a completely different way from SMS. Initially, the sending device encodes the multimedia content in a fashion similar to sending a MIME e-mail (MIME content formats are defined in the MMS Message Encapsulation specification). The message is then forwarded to the carrier's MMS store and forward server, known as the MMSC. If the receiver is on another carrier, the relay forwards the message to the recipient's carrier using the Internet.
Once the MMSC has received a message, it first determines whether the receiver's handset is "MMS capable", that is, it supports the standards for receiving MMS. If so, the content is extracted and sent to a temporary storage server with an HTTP front-end. An SMS "control message" containing the URL of the content is then sent to the recipient's handset to trigger the receiver's WAP browser to open and receive the content from the embedded URL. Several other messages are exchanged to indicate status of the delivery attempt. Before delivering content, some MMSCs also include a conversion service that will attempt to modify the multimedia content into a format suitable for the receiver. This is known as "content adaptation".
If the receiver's handset is not MMS capable, the message is usually delivered to a web based service from where the content can be viewed from a normal internet browser. The URL for the content is usually sent to the receiver's phone in a normal text message. This behaviour is usually known as the "legacy experience" since content can still be received by a phone number, even if the phone itself does not support MMS.
The method for determining whether a handset is MMS capable is not specified by the standards. A database is usually maintained by the operator, and in it each mobile phone number is marked as being associated with a legacy handset or not. It can be a bit hit and miss since customers can change their handset at will and this database is not usually updated dynamically.
E-mail and web-based gateways to the MMS (and SMS) system are common. On the reception side, the content servers can typically receive service requests both from WAP and normal HTTP browsers, so delivery via the web is simple. For sending from external sources to handsets, most carriers allow MIME encoded message to be sent to the receiver's phone number with a special domain. An example of this would be PTN@messaging.carrier.com, where PTN is the public telephone number. Typically the special domain name is carrier specific.
You can find out more about MMS and its history here: http://en.wikipedia.org/wiki/Multimedia_Messaging_Service.