is it possible to input tonemarks in Vietnamese mobile phone

[Young]

I know the PC keyboard layout of Vietnamese but don't know of mobile phone's keypad of soft keyboard.
I'm about to develop a Vietnamese input application for the Windows mobile phone, so I need the layout and actual method of input.
Let me know how to input Vietnamese in mobile phones.
Especially about tone marks.

I'm longing to hearing your precious helps!

[Tenebrarum]

I did make something like a guide to the Vietnamese cellphone keyboard in this post. Hope that helps.