The equivalent of the 770 case mode is to press the 'I' button followed by the center of the 5-way pad (or use the stylus).
However, you must set two timeouts to be the same: In the control panel, select screen and set both to the same value. (This is reported as a bug in bugzilla). After that, pressing the two buttons will immediately lock the screen and turn off the display. Edit: This doesn't turn off wi-fi unless you have specified it to, but I believe this is the same for the 770 - you don't want it off anyway, it doesn't use much power and someone can still contact you in voip/chat.