Design Proposal for a Dynamic Bottom (Task)Bar for Plasma Mobile

Vision

Permanently visible navigation bars at the bottom of the screen (like in Android) occupy screen space for little functionality (for example, switching between application still needs to switch to a different mode). A dynamic bottom bar which can vary in height from 0 (invisible) to half the screen height offers a much improved space : functionality ratio

Scenarios

Berna is fully immersed in reading an article on the web. The more space she has to display the article, the easier it is to read it, so she'd like as little else to be on the screen has possible
While reading the article on the web, Berna has a question to ask her boss over the phone, so she is looking for the quickest way to start the call app.
Santiago is discussing a website with a colleague over instant messaging. For that, he has to regularly switch between the browser and the IM application, and appreciates a quick way to do this. with as little actions as possible