Make Simple Social Icons a little more awesome with FontAwesome.

functions-alt.php

<?php

// do NOT include the opening tag

add_filter( 'simple_social_default_glyphs', 'rgc_simple_social_icons_glyphs' );
function rgc_simple_social_icons_glyphs( $glyphs ) {
	$glyphs = array(
		'bloglovin'   => '<span class="fa fa-heart"></span><span class="screen-reader-text">Bloglovin</span>',
		'dribbble'    => '<span class="fa fa-dribbble"></span><span class="screen-reader-text">Dribbble</span>',
		'email'       => '<span class="fa fa-envelope"></span><span class="screen-reader-text">Email</span>',
		'facebook'    => '<span class="fa fa-facebook"></span><span class="screen-reader-text">Facebook</span>',
		'flickr'      => '<span class="fa fa-flickr"></span><span class="screen-reader-text">Flickr</span>',
		'github'      => '<span class="fa fa-github"></span><span class="screen-reader-text">Github</span>',
		'gplus'       => '<span class="fa fa-google-plus"></span><span class="screen-reader-text">Google+</span>',
		'instagram'   => '<span class="fa fa-instagram"></span><span class="screen-reader-text">Instagram</span>',
		'linkedin'    => '<span class="fa fa-linkedin"></span><span class="screen-reader-text">Linkedin</span>',
		'pinterest'   => '<span class="fa fa-pinterest"></span><span class="screen-reader-text">Pinterest</span>',
		'rss'         => '<span class="fa fa-rss"></span><span class="screen-reader-text">RSS</span>',
		'stumbleupon' => '<span class="fa fa-stumbleupon"></span><span class="screen-reader-text">Stumbleupon</span>',
		'tumblr'      => '<span class="fa fa-tumblr"></span><span class="screen-reader-text">Tumblr</span>',
		'twitter'     => '<span class="fa fa-twitter"></span><span class="screen-reader-text">Twitter</span>',
		'vimeo'       => '<span class="fa fa-vimeo-square"></span><span class="screen-reader-text">Vimeo</span>',
		'youtube'     => '<span class="fa fa-youtube"></span><span class="screen-reader-text">Youtube</span>',
	);

	return $glyphs;
}

functions.php

<?php

// do NOT include the opening tag above

add_action( 'wp_enqueue_scripts', 'rgc_simple_social_icons_fontawesome' );
/**
 * Enqueue FontAwesome stylesheet
 */
function rgc_simple_social_icons_fontawesome() {
	wp_enqueue_style( 'fontawesome', '//maxcdn.bootstrapcdn.com/font-awesome/4.3.0/css/font-awesome.min.css', array(), '4.3.0' );
}


add_filter( 'simple_social_default_css', 'rgc_simple_social_icons_css' );
/**
 * Replace Simple Social Icons' stylesheet
 */
function rgc_simple_social_icons_css( $css_file ) {
	$css_file = get_stylesheet_directory_uri() . '/simple-social-icons.css';
	// $css_file = ''; // alternate method: if you want to just add your styling to your theme styesheet

	return $css_file;
}

add_filter( 'simple_social_default_glyphs', 'rgc_simple_social_icons_glyphs' );
/**
 * Replace Simple Social Icons's glyphs with FontAwesome
 */
function rgc_simple_social_icons_glyphs( $glyphs ) {
	$glyphs = array(
		'bloglovin'   => '<span class="fa fa-heart"></span>',
		'dribbble'    => '<span class="fa fa-dribbble"></span>',
		'email'       => '<span class="fa fa-envelope"></span>',
		'facebook'    => '<span class="fa fa-facebook"></span>',
		'flickr'      => '<span class="fa fa-flickr"></span>',
		'github'      => '<span class="fa fa-github"></span>',
		'gplus'       => '<span class="fa fa-google-plus"></span>',
		'instagram'   => '<span class="fa fa-instagram"></span>',
		'linkedin'    => '<span class="fa fa-linkedin"></span>',
		'pinterest'   => '<span class="fa fa-pinterest"></span>',
		'rss'         => '<span class="fa fa-rss"></span>',
		'stumbleupon' => '<span class="fa fa-stumbleupon"></span>',
		'tumblr'      => '<span class="fa fa-tumblr"></span>',
		'twitter'     => '<span class="fa fa-twitter"></span>',
		'vimeo'       => '<span class="fa fa-vimeo-square"></span>',
		'youtube'     => '<span class="fa fa-youtube"></span>',
	);

	return $glyphs;
}

screen-reader.css

/* Screen Readers
------------------------------- */

.screen-reader-text,
.screen-reader-text span,
.search-form label {
	clip: rect(0, 0, 0, 0);
	height: 0;
	position: absolute;
	width: 0;
}

simple-social-icons.css

.simple-social-icons {
	overflow: hidden;
}

.simple-social-icons ul {
	margin: 0;
	padding: 0;
}

.simple-social-icons ul li {
	float: left;
	margin: 3px;
	padding: 0;
	border: none;
	background: none;
	list-style-type: none;
}

.simple-social-icons ul li a {
	display: inline-block;
	box-sizing: content-box;
	width: 1em;
	border: none;
	font-family: "fontawesome";
	font-weight: normal;
	font-style: normal;
	font-variant: normal;
	-webkit-font-smoothing: antialiased;
	-moz-osx-font-smoothing: grayscale;
	line-height: 1em;
	text-align: center;
	text-decoration: none;
	text-transform: none;

	speak: none;
}

.simple-social-icons ul.aligncenter {
	text-align: center;
}

.simple-social-icons ul.aligncenter li {
	display: inline-block;
	float: none;
}

Relevant ticket: osompress/simple-social-icons#4