Gruntfile

module.exports = function(grunt) {

    grunt.initConfig({
        seo: {
            site: 'index.html'
        }
    });

    grunt.loadTasks('grunt-contrib-seo/tasks');

    grunt.registerTask('default', ['seo']);
};

main.js

//var url = phantom.args[1];

var page = require('webpage').create();
var url = 'http://www.phantomjs.org/';
page.open(url, function (status) {
    //grunt.log.write('wohooo page loaded');
    //Page is loaded!
    phantom.exit();
});

seo.js

/*
 * grunt-contrib-seo
 *
 * Copyright (c) 2013 Christoph Burgdorf, contributors
 * Licensed under the MIT license.
 */

'use strict';

module.exports = function(grunt) {

    var fs          = require("fs"),
        path        = require("path"),
        phantom     = require("grunt-lib-phantomjs").init(grunt);

    grunt.registerMultiTask('seo','fetch html snapshots', function(){
        debugger;

        phantom.spawn('index.html', {
            // Additional PhantomJS options.
            options: {
                phantomScript: "main.js"
            },
            // Complete the task when done.
            done: function (err) {
                grunt.log.write('wohooo done');
            }
        });

        grunt.log.write('wohooo');
    });
};