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/MMS messages are texts and photos that you send to other cell phones or iOS devices. These messages appear in green text bubbles on your device. To use SMS/MMS, you need a text-messaging plan. Contact your carrier for more information. If Wi-Fi is unavailable, iMessages will be sent over cellular data.