> That's driven by screen size - there's simply not enough screen real estate on a phone to label every button with words. It does have a legit discoverability problem, which most folks in UX acknowledge but don't know how to fix, given other constraints of the media.

Some of the most effective solutions to this I've seen require solutions beyond visual representation. They address the problem through dimensions independent of viewport size and space.

For example, LukeW's "Don't Divert the Train" http://www.lukew.com/ff/entry.asp?1798 moves content from behind navigation and into the user's already-occurring action stream. The button is removed entirely, as is the designer's need to consider how communicative icons are for representing actions.

This requires a broader view of how features relate to each other through a design process that discovers other paths to successful behavior. Approaches like the hamburger menu, in addition to the usability issues you note, solve functional goals but have fallen out of vogue for their ineffectiveness at encouraging specific actions. Label-less icons, while attractive and convenient, suffer similar problems. As getting users successful quickly is generally an important goal (before they've internalized your app's unique visual language), the current trend of putting core functionality behind opaque symbols seems counterproductive.