Thanks tom.
that made guest to view the contacts but it also enables them to edit add or delete the contacts which is not required. i need only admin to have those permissions.
it will be really help full if you can help me with this part.

To disable the editing option for non-administrators, open web/staff/app/cls_ps_(--table-name--).inc.php and add

if ( !$this->sys->IsAdmin() ) exit;

after

case 'edit_inp':

The result should look like:

case 'edit_inp': if ( !$this->sys->IsAdmin() ) exit;

Do the same for the following lines, too.
"case 'edit_done':"
"case 'reg_inp':"
"case 'reg_done':"
"case 'del_multi':