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.
The SMS standard. The SMS standard defines what information is sent in a text message, what bits of binary code make up each letter, and how this data is organised so that sending and receiving devices can communicate with each other.