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.
SMS is a stateless communication protocol in which every SMS message is considered entirely independent of other messages. Enterprise applications using SMS as a communication channel for stateful dialogue (where an MO reply message is paired to a specific MT message) requires that session management be maintained external to the protocol.