Well, there is a "risky" way to change the root (or the mobile) password:
perl -e 'print crypt("MYPASSWORD", "XU");'
Where MYPASSWORD is the new password you want, and XU is a random two-letter salt of your choice. Copy the encrypted output and replace the existing one in /etc/master.passwd on the phone.
For example, if you put alpine (in place of MYPASSWORD) and /s (in place of XU) you should get /smx7MYTQIi2M. Try it out to get a feel for it, then pop in your own choice of password and two character "salt".
I can't remember where I found the basis for these instructions, but I've used them and they work.