WCF 4 Rest Getting IP of Request?

Hey, how do you get the IP address of the person making a request in something like the following:

    [ServiceContract]    
    [AspNetCompatibilityRequirements(RequirementsMode = 
    AspNetCompatibilityRequirementsMode.Required)]    
    [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)]        
    public partial class UsersService
    {                          
        [WebInvoke(UriTemplate = "", Method = "PUT")]        
        public User AddNewUser(User newUser)
        {            
            // code goes here including GETTING AN IP??
        }

Thanks!