how to make fake sender number

[Ahmad Munif]

i'm using siemens m35 as virtual smsc,
i'm building user interface to send sms via web,
the item are from,to,text.
i'm using this script to send sms:
        $url= sprintf('/cgi-bin/sendsms?username=user&
              password=pass&from=%s&to=%s&text=%s',
              $from,$to,urlencode($text))

that interface can send successfully, but from item can't change to user
number, but always using my phone number (m35 as smsc).

how to change global number to any number that i want ?.