Hi, if you want to send pictures and logos so siemens mobile phones it is very important that you set the coding of the message to 8 Bit. Set the paramater CODING=2 while using the HTTP interface. There is no UDH string, all the SEO strings are in the parameter TEXT. There is a strict reglementation how to create such SEO strings, you can find a documentation at Siemens web page (look for Specification for OTA Download Services).
-- Greeting Thorben Hischke