You can add a button by inserting below HTML web resource into the form:-
<html><head>
<meta charset="utf-8">
<title></title>
<style type="text/css">
#Button1 {
width: 167px;
}
</style>
</head><body style="width: 134px;">
<p>
<input id="SaveCall" onclick="parent.createPhonecall()" value="Save Phonecall" type="button"></p>
</body></html>
create a function named createPhonecall and use it onload of form
Regards Faisal