after

    // Start building the command object.
    var command = {
        className: service,
        methodName: action,
        arguments: []
    };

    // Register the callbacks and add the callbackId to the positional
    // arguments if given.
    var callbackId = null;
    if (successCallback || failCallback) {
        callbackId = service + PhoneGap.callbackId++;
        PhoneGap.callbacks[callbackId] = 
            {success:successCallback, fail:failCallback};
        command.arguments.push(callbackId);
    }

before

    // Register the callbacks if given.
    var callbackId = null;
    if (successCallback || failCallback) {
        callbackId = service + PhoneGap.callbackId++;
        PhoneGap.callbacks[callbackId] = 
            {success:successCallback, fail:failCallback};
    }

    // Build the command object.
    var command = {
        className: service,
        methodName: action,
        arguments: [callbackId]
    };