Multimedia SMS, also referred to Multimedia Messaging Service or MMS, is a enhanced version of Short Message Service text messages. MMS offers enhanced content delivery, making it not unlike email between phones. However, MMS is a more costly messaging service and may not be supported on all phones. In comparison, SMS has been fine-tuned over a longer period of time, and is supported on all phones.
The most significant advantage of MMS over SMS is multimedia content. SMS only supports text, whereas MMS supports images, videos and audio in your message. MMS messages can include photos and videos recorded on your phone or media added to your phone from your computer. On some phones you can use emoticons via MMS. This higher level of personalization allows you to deliver voice messages and add more context to your message than using text alone.
SMS messaging limits your messages to 160 characters -- including spaces and punctuation. MMS messaging not only allows you to embed more styles and format your text, but also allows significantly longer messages between phones. There is not a set character limit for MMS, though your phone may apply one. Being able to send a longer message makes MMS a more effective method of communication when email isn't available, such as on feature phones that don't offer Internet access.
The effectiveness an MMS message depends on the recipient's phone; what may be an entertaining video for someone with an iPhone may be too hard to watch for someone with a feature phone. Pictures taken with different resolutions or dimensions may be hard to view on a different display, with corresponding loss of detail. Sound on your recipient's phone may not as be as clear as on your phone.
Unless you've explicitly asked, you have no way of knowing if your recipient has a phone that supports MMS. Although smartphones with multimedia support are becoming commonplace, many people still use feature phones. Beyond that, not everyone has MMS enabled on their plan. Different phones may support different media types as well; the format your phone records a video in, for instance, may not be playable on your recipient's phone.
Sending and receiving MMS messages may cost more on your plan and your recipient's plan, especially if text messages are paid per message. Costs vary depending on your cellular plan; some may define the MMS cost per message, while others do it per kilobyte. Messages are charged to both the sender and recipient. Check with your carrier to understand any costs associated with MMS.