How to display Contact Summary address in an Activity Form?
Like Jon G suggested a little more information would help a lot, I am now assuming I understand what you mean but I do not really :-)

Obviously it is possible to place the address on the activity form (I am assuming you mean the form of the activity when you click 'edit'/'view'? But you can not do this from the UI, you will need to do some customization.

My way would be to write a little extension and use the CiviCRM buildForm hook to add the address on the list of form variables, and add a little jQuery to the template (using CRM_Core_Region::instance('page-body')-&gt;add(array('template' =&gt; 'yourtemplatewithjQuery.tpl'). This answer assumes you are familiar with PHP and jQuery and with concepts like CiviCRM extensions and hooks. If you are not, the place to start would be the CiviCRM Documentation at http://wiki.civicrm.org/confluence/display/CRMDOC/CiviCRM+Documentation.

ALternative would be to add jQuery to your own .tpl, retrieve the Contact Address with the CRM.api3 function and then display the address. Example of the CRM.api3:

CRM.api3('Contact', 'get', params).done(function(result) {
         &lt;your function&gt;
        })