Vodafone, a big mobile operator based in Britain, sees mobile advertising as a potentially lucrative source of additional income.

ECONOMIST: Mobile advertising

Each variety of lace has long been created by rural women as a source of additional income and has left a permanent mark on the culture of its region.

UNESCO: Culture

Jobs creation is a far healthier and more sustainable source of additional disposable income than increases in home equity values.

FORBES: How Important Is A Housing Recovery?

An additional source of cash also resulted from front running of bonus income and other income into December, 2012 to avoid the tax hikes.

FORBES: Huge U.S. Equity Fund Inflows Being Funded By Tax Front Running Income