jQuery Forum

If you want more than 5 items then you need to build and style the navbar yourself.

From http://jquerymobile.com/demos/1.2.0/docs/toolbars/docs-navbar.html

If more than 5 items are added, the navbar will simply wrap to multiple lines:

You didn't specify if you're building a phone or tablet application or both.  I would suggest carefully considering what you're presenting in your navbar if you need more than 5 items as it isn't likely to fit well on smaller screens.  Not all consumers have the latest and greatest devices with 5"+ screens.  Don't forget about your users that may be on older devices that don't have the screen real estate of the latest and greatest phones/tablets.  A navbar with six items may end up being too small and difficult to use on older devices with limited screen real estate (think about some of the BlackBerry devices).

If you have a need to present a large number of options you might need to rethink your application layout and navigation model.  Mobile users are typically interested in accomplishing a very specific task to improve their productivity and don't necessarily need/want the entire kitchen sink.  If you need to provide that many options/buttons, perhaps consider using something like a select menu and listen for change events to perform an operation or function.  This would work well on devices of all sizes.