web service calling?

Hello,
Can web service be called only through javascript ?
can i call it on OnClick event of button without using javascript?..
can u plz give some small example of syntax to call web service?

here is my webservice :
 
<%@ WebService Language="VB" CodeBehind="~/App_Code/service.vb" Class="service" %>


Imports System.Web
Imports System.Web.Services
Imports System.Web.Services.Protocols

<WebService(Namespace:="http://tempuri.org/")> _
<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Public Class service
     Inherits System.Web.Services.WebService

    <WebMethod()> _
    Public Function HelloWorld() As String
        Return &qu ...