Question : Why HTTP_X_UP_SUBNO is null????

Hello everyone!
I'm a chinese and so sorry because my English is poor.
I have a question now.
It must obtain the indentify of mobile,as far as know
variable HTTP_X_UP_SUBNO memories the infomation of
the mobile,but it is null in my php pages.
  How can I do???
  Who have the answer?please email to [email protected] or [email protected] .
  Thank you!!!!!!

Answer : Why HTTP_X_UP_SUBNO is null????

X_UP_SUBNO is usually used by Openwave browsers. Check what browser your phone is using. If it's from AU, Nokia or Access it will NOT use  X_UP_SUBNO.