The following function is called in the zimlet init function, but when create a new mail or open a mail, the new button doesn't show up. No exception reported from the browser, any help is greatly appreciated.

com_zimbra_scs.prototype._addButtons =
// Add the Salesforce Button to the Compose Page
this._composerCtrl ="GetComposeController");
this._composerCtrl._scs = this;

this._toolbar = this._composerCtrl._toolbar;

// Add button to toolbar
ZmMsg.scsAdd = "Call";
ZmMsg.scsTooltip = "Call the sender.";
var op = {text: "scsAdd", tooltip: "scsTooltip", image: ""};
var opDesc = ZmOperation.defineOperation(null, op);
ZmOperation.addOperation(this._toolbar,, this._toolbar._buttons, 1);
this._toolbar.addSelectionListener(, new AjxListener(this._composerCtrl, this._CallSender));

com_zimbra_scs.prototype._CallSender= function(ev) {
var msg = this._composeView.getMsg();