function MM_openBrWindow(theURL,winName,features) { //v2.0
  window.open(theURL,winName,features);
}

function abreChat(){
    MM_openBrWindow('http://www.easychat.com.br/easy/iframe_w33.php?chat_id=1875&clie_id=1818&check_sum=5511','Atendimento','width=350px,height=650,status=no,scrollbars=yes,resizable=yes');
}