XF 1.5 Font family - mobile devices

Today, after some startup problems, our forum moved from PHPBB to xenForo.
Something we should have done earlier....

We changed a lot via the templates and color palets.
Only thing which is bugging me, is the font family on mobile devices.
I changed almost all font families of all css files (perhaps not the smartest thing to do... but I'm learning here :) ). But my mobile devices (phone and tablet) still give me a 'Times New Roman" as default font on the message body.
Is there a way to change this?
Just checked; Nope.
No. I wanted to force the preferred font.
Due to your reply, it is clear to me that this does not work.
What do you advise?
And don't get me wrong; I did search extensively, but did not find the answers I was looking for. Now with your reply, I have more search options :)

Thanks, Brogan (y)

By the way: why are font names sometimes tagged by quotes and others are not?
E.g.: "Palatino Linotype", "Book Antiqua", Palatino, serif
Thanks, Brogan.
I just left that page and decided to take a web save font and a fall-back.
Issue with my mobile devices is solved with this solution/answer.
If I'm feeling better (having the flu atm) I will do three cheers for you :ROFLMAO: