Canonical has ported Ubuntu to smartphones and is working on the Ubuntu Edge smartphone.
Android is based on Linux as well, but Ubuntu might have more free and open source apps ported to it. The Ubuntu Edge might take a few years to catch on, but they already have a Kickstarter even for under $700 to buy one. They seem close to meeting their goal.
With the Ubuntu Edge you have a smartphone that has the abilities of a PC running Ubuntu Linux. On the Android you have that if you run a special Ubuntu app that installs Ubuntu under Android. The iPhone not so much.
Once the major cell phone carriers sell the Ubuntu Edge it will start to catch on. Since Ubuntu is free and open sourced, any tablet or smartphone can be made to run it. In case of Apple vs. Android lawsuits, all Android phones can be ported to Ubuntu.