Font Awesome is fully open source and is GPL friendly. You can use it for commercial projects, open source projects, or really just about whatever you want.
Attribution is no longer required as of Font Awesome 3.0 but is much appreciated: "Font Awesome by Dave Gandy - http://fontawesome.io".Font License
[list]Applies to all desktop and webfont files in the following directory: font-awesome/fonts/.License: SIL OFL 1.1URL: http://scripts.sil.org/OFL
[list]Applies to all CSS and LESS files in the following directories: font-awesome/css/, font-awesome/less/, and font-awesome/scss/.License: MIT LicenseURL: http://opensource.org/licenses/mit-license.html
[list]Applies to all Font Awesome project files that are not a part of the Font or Code licenses.License: CC BY 3.0URL: http://creativecommons.org/licenses/by/3.0/
[list]All brand icons are trademarks of their respective owners.The use of these trademarks does not indicate endorsement of the trademark holder by Font Awesome, nor vice versa.Brand icons should only be used to represent the company or product to which they refer.Please do not use brand logos for any purpose except to represent that particular brand or service.