Can we call submit handler of one form into another form?
You could pass the page number as argument to your hook_menu()

&lt;?php    
function mymodule_menu() {
    $items['abc/def/%'] = array(
      'page callback' =&gt; 'mymodule_abc_view',
      'page arguments' =&gt; array(2),
    );
    return $items;
  }


Then if it is step-one for example, get your subscription plan form, render it then submit.
In the submit function use:

 &lt;?php
// Force the form to rebuild. If we do not do this, the value(s) in $form_state['storage'] will be lost
$form_state['rebuild'] = TRUE;
//Redirect to step two
$form_state['redirect'] = 'abc/def/2';


In step 2 get the user profile so that in the next submission you'll have the data from both forms in the submit function.