I'm trying to use Ip Telephony and integrate Twilio in Salesforce
So now the issue is how to enable click to dial option
I have already have call center configured and embedded iframe is shown up 
 Iframe -its  a visual force page  with button that should enable click to dial option and it have callback that should respons wether all ok or not and pop up  alert wether its enabled or not 
But when I'm clicking on the "enable click to dial" button nothing happens
No phones enabled to be dialed no any alerts, no exaptions in console, so callback event does not invoked

Code mark up
 

<apex:page controller="TwilioClientController" showHeader="false" >
   <script type="text/javascript" src="//static.twilio.com/libs/twiliojs/1.2/twilio.min.js"></script>
    <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>
    <script src="/support/api/37.0/interaction.js"></script>
function enableClickToDial() {
    sforce.interaction.cti.enableClickToDial(function (response) {
        if (response.result) {
            alert('Click to dial was enabled.');
        } else {
           alert('Click to dial was not enabled.');
        }
        alert(response.error);
    }
);
}
<button onclick="enableClickToDial();">enable click to dial</button>
</apex:page>

Similar example from open cti api 
https://developer.salesforce.com/docs/atlas.en-us.api_cti.meta/api_cti/sforce_api_cti_enableclicktodial.htm