'Add Phone Call' functionality using custom button on the form.

Hello,

I have added a button on the form using a web resource. 

My requirement is to Open a 'Add Phone Call' window when this button is clicked, just like when Add Phone call button is clicked on the social pan or ribbon.

Is it possible by using javascript? 

I tried calling the method Mscrm.AddActivity.addActivityToForm(4210,null) on button click but I got an error that Mscrm is undefined.

Any help would be appreciated.

Thanks,

Priyank