Top Tip for RWD: Forget about targeting specific devices.
Make the breakpoint where you think it needs to be, that is the point when the columns look uncomfortably tight.
Example:-
@media screen and (min-width: 700px) {
#content-wrapper {
display: table;
width: 100%;
}
#content-wrapper div { display: table-cell; }
#column3 { width: 20%; }
}
This being mobile first (not normally my style, but makes sense here) remove these from the ‘default’ css before the query.