In order to send SMS messages containing ringtones, wallpapers, WAP push or vCards, the content needs to be sent as a binary message. In order to send a binary message to a phone, the User Data Header (UDH) construct must be used. The UDH is a short hexadecimal code which, when received by the handset indicates the type of content contained in the binary message and how to process it. In addition to the UDH, setting the correct Data Coding Scheme (DCS) value, 0x04 or 4 in the case of a binary SMS is also required.
