With the Messages app and the built-in iMessage service, you can send unlimited text messages over Wi-Fi to others using iOS 5 or later, or OS X Mountain Lion or later. Messages can include photos, videos, and other info. You can see when other people are typing, and let them know when you’ve read their messages. iMessages are displayed on all of your iOS devices logged in to the same account, so you can start a conversation on one of your devices and continue it on another device. For security, iMessages are encrypted before they’re sent.
WARNING: For important information about avoiding distractions while driving, see Important safety information.
Note: Cellular data charges or additional fees may apply for iPhone and iPad users you exchange messages with over their cellular data network.