Binary SMS Messages
Binary SMS messages allow sending of various types of rich-content, such as transferring ringtones, telephone system settings and WAP-Push via text messaging.
Any binary SMS message has 140 bytes of data which can be used. This data is split into two distinct parts - the user data header (UDH) and the message data. UDH notifies mobile phones about the type of data in the message, defining the type of content being sent.