You should automatically see the mobile version of the message board when using your cell phones and other mobile devices, however if you do not you can manually change to the mobile theme version. At the bottom of every page of the board is a link called "Change Theme". Click it and select "IP.Board Mobile" to see the mobile version.
To go back, you can click the "Change Theme" button again and set back to "ChitChat".
The big difference is the mobile theme is blue, the regular ChitChat theme is purple.