Getting a value from controller extension to Visualforce page

I've been wondering about this alot. I have a VF page that has a StandardController for Contact and a custom extension that handles an external webservice call. This extension class contains a string value that the web service call sets and then I need to pass that value to the VF page for display. This value is not bound to any field in SF but is rather just a string value. I'm trying to use actionFunction to do this, since it seems easier than using JS Remoting (my JS callback function skill level is not high)

VF Page:

 <apex:page showHeader="false" sidebar="false" standardController="Contact" extensions="CallStatus">


<apex:form >
<apex:actionFunction name="gomob"  action="{!GetCallStatus}" reRender="amount"/>
<div id="black">


<apex:outputpanel id="amount">
            <apex:outputText value="Get Status!: {!amount}"/>
            <apex:actionSupport event="onclick" 
                                action="{! GetCallStatus}" 
                                rerender="amount" status="whileStatus"/>
        </apex:outputpanel>
        <apex:actionStatus id="whileStatus" 
                           startText=" (fetching...)" 
                           stopText=" (done)"/>

</div>
</apex:form>
</apex:page>

My extension class:

global class CallStatus {

    private final ApexPages.StandardController controller;
    public WS_GoMobileStatus(ApexPages.StandardController controller){
    this.controller = controller;
    }

    global String kId { get; set; }
    transient String amount {get; set;}
    Contact con;

    public CallStatus(){


    }

    Public String GetCallStatus(){
    String conId = ApexPages.currentPage().getParameters().get('Id');
    con = [SELECT Id,kid__c from Contact where Id =:conId LIMIT 1];
    ktId = con.kid__c;

        String endp = 'ENDPOINT_URL?action=GetCallStatus&kid=';


         HttpRequest req = new HttpRequest();
         req.setMethod('GET');
         req.setHeader('Content-Type','application/json; charset=utf-8');
         req.setHeader('User-Agent', 'force.com');
         req.setEndpoint(endp+=ktId);

         Http http = new Http();
         System.HTTPResponse res = new System.HTTPResponse();

          try {

        //Execute web service call here     
        res = http.send(req);       



        //Helpful debug messages
        System.debug(res.toString());
        System.debug('STATUS:'+res.getStatus());
        System.debug('STATUS_CODE:'+res.getStatusCode());

} catch(System.CalloutException e) {
    //Exception handling goes here....
}       

        amount = res.getBody();
        return amount;


    }
}

Is my use of the transient keyword wrong here? When I refer the {!amount} in the VF page, I get the error Error: Unknown property 'ContactStandardController.amount

Is t not possible to have the extension class return the String value to the VF page?