Take one minute of video. Look at the file size. Now how many of these 1 minute files can you fit onto an 8GB card in your particular format and camera/device.
SMS stands for Short Message Service, which is the formal name for text messaging. It's a way to send short, text-only messages from one phone to another. These messages are usually sent over a cellular data network. That's not always true, though, as in the case of iMessage below.
What is the difference between MMS and SMS messaging? There is a broad difference between MMS messages, and SMS texts sent to a recipient. MMS, or Multimedia Messages, usually contain some sort of visual component, like a picture or video, that helps to sell a product.