SMS is the technical name for mobile phone text messaging. The original specification called for SMS messages to be only the length of 160 characters. As popularity of SMS increased the ability to send text messages that appear longer than 160 characters was created. Behind the scenes, SMS never sends a single text message greater than 160 characters. Instead, multiple SMS messages are tied together to make longer texts. The sending phone sends the message parts with a header that keeps the messages in order. The receiving phone determines how to display the segments. Most current phones display the message as one long message in proper order. But it gets more confusing from here. Each segment in a multi-part message doesn't actually contain those 160 characters from the intial SMS specification. Since the header which records each part's position on the message as a whole is sent, this takes up exactly 7 characters of the 160-character long segment. So once you send an SMS that is longer than 160 characters you are actually sending multiple 153-character messages stiched together. 1,600 overall characters is the maximum number of characters that can be sent in "one" text message on EchoBack.