If you think people in undeveloped countries need to generate power from their urine to charge their cell phones, you really need to get out and see the world.
For this reason, countries like Ecuador, Guatemala, etc. Have cell phone rates higher than developed countries like Australia and the US. http://en.wikipedia.org/wiki/List_of_countries_by_number_of_...
Developing countries don't skip technologies out of a desire for hopscotch or something. They skip wired tech because copper wires are expensive, their expense doesn't go down over time in contrast with the increasing sophistication of chips. Conventional phone lines and electrical power are both wired tech. Thus both are harder in third world conditions.
But electrolyzing water, and then burning hydrogen is a net loss in energy, and the 3% urea does not give enough advantage to offset this.
Maybe if you had some way to preferably electrolyze just the urea and leave the water alone, but then you have to deal with batch process (instead of just continually adding liquid), and the lower voltage makes the reaction too slow.
[0] http://www.suttonfruit.com/pics/urea_electrolysis.pdf
edit: grammer
The only good reason to extract hydrogen is for storage. For example, solar energy could be used to extract the hydrogen from urea, which could then be burned at night to continue to generate power.
On it's own, any technology that requires extraction of hydrogen will result in a net loss. Sometimes a HUGE net loss.
If you can do it efficiently enough, in theory electrolyzing urea then burning it to water (and nitrogen) is a net gain in energy.