In small businesses - often the best foot in the door for open source software is a pet project, something you can do transparently to design something to show management about the advantage of the software has over more traditionally licensed fare. Being able to speak the language of IT management helps - Cost of Ownership, Return on Investment, being able to present facts based on license costs is also helpful - management listens to dollars and sense, followed by legality.
Of course, if your business deals with large vendors who have a stake in keeping things locked to Microsoft, Oracle, IBM or HP - you are fighting a steeply uphill battle.