wpquestions.com, ID = 3159

function custom_list_terms( $taxonomies = array( 'category' ) , $args = array() ) {

    // vars
    $r = '';
    $letter = '';

    // get all terms
    $terms = get_terms( $taxonomies, $args );

    // if there are any temrs
    if ( $terms ) {

        // begin building output
        $r .= '<h2>' . $letter . '</h2>';
        $r .= '<ul class="term-archive letter-' . $letter. '">';

        // set the topmost letter to the first letter of the first term
        // $letter = mb_strtoupper( mb_substr( $terms[0]->name, 0, 1 ) ); // use this when working with non-ASCII characters
        $letter = strtoupper( substr( $terms[0]->name, 0, 1 ) );

        // loop terms
        foreach ($terms as $term) {

            // re-assign letter variable
            $old_letter = $letter;

            // get first letter of term name
            // $letter = mb_strtoupper( mb_substr( $term->name, 0, 1 ) ); // use this when working with non-ASCII characters
            $letter = strtoupper( substr( $term->name, 0, 1 ) );

            // check wether we're at a new letter
            if( $letter != $old_letter ) {

                // start a new section for new letter
                $r .= '</ul>';
                $r .= '<h2>' . $letter . '</h2>';
                $r .= '<ul class="term-archive letter-' . $letter . '">';

            }

            // sets term meta (to an empty string if function doesn't exist)
            $term_meta = function_exists( 'get_terms_meta' ) ? get_terms_meta( $term->term_id, 'mysummary', true ) : '';

            // HTML for each term
            $r .= '<li class="' . $term->taxonomy . '">';
            $r .= '<a href="/statistics/term/' . $term->slug . '" title="' . sprintf( esc_attr__( 'View all post filed under %s' ), $term->name ) . '">';
            $r .= $term->name;
            $r .= '</a> ';
            $r .= '(' . $term->count . ')';
            $r .= $term_meta; // the term meta can be appended to the HTML like this
            $r .= '</li>';

        }

        $r .= '</ul>';

        // echo/return the result
        echo $r;

    }

}