Actually, I misspoke - jQuery Mobile
does have a "grid" widget. It's something I don't like and
don't use, because (at least in the past, not sure about
1.4) it is (was) a clunky, heavy (generates lots of markup) solution.
That comes from trying to work on all browsers.
But there's an example in the docs of
doing what you want:
It's easy enough, though, to layout any
elements either side-by-side or stacked vertically with a bit of CSS.
In fact, the example pages do that. (Oops, they used to, before 1.4!)
Take a look at the "quick nav" sidebar in the demo pages.
Narrow your browser. Notice that it goes away. In the 1.4 demo, it's
then accessible using a panel, but in older demos, it was stacked
below the content.
That's just responsive CSS.
I think the page flow module is the holy
grail here, but just not implemented in enough browsers yet to
actually use. When it's adopted by iOS and Android browsers, you will
see the use take off, since now there will be many PhoneGap apps using
it (since they don't have to worry about supporting old browsers.)