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.
Short Message Service (SMS) is a text messaging service component of most telephone, World Wide Web, and mobile telephony systems.[1][1] It uses standardized communication protocols to enable mobile phone devices to exchange short text messages.