OK,
Suppose you have a menu set up with parents and children:
Menu name is mymobilemenu
entries are
Parent1
Child11
Child12
Parent2
Child21
Parent3
then you would
extensions >module manager
put menu in the filter and click go so that you can see the menu modules.
edit the one for the iphone. (mod_mj_iphone_menu )
enable
position mj_iphone_middle
menu assignment menus * all
parameters > Module Parameters
on the drop down for menuname select mymobilemenu.
save
now when you view the site using the iphone temlate you will see
Parent1
Parent2
Parent3
when you click on Parent1 you will see
Child11
Child12
You will need to do the same for the 3 other types (XHTML, Imode, WAP)
The other templates, for the other types of mobile, show the child items below,
so
Parent1 Parent2 Parent3
click on Parent1 you will still see the 3 Parents
and the Children of the Parent1
Parent1 Parent2 Parent3
Child11 Child12
Hope this helps.