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.
edit Definitions. SMS is the abbreviation for Short Message Service and is the text communication service component of a phone or mobile communication system, using standardized communications protocols that allow the exchange of short text messages between fixed line or mobile phone devices.