Using Extension Methods In Static Methods On Extended Classes?

I have an extension method as follows:

public static class PageExtensions
{
public static int GetUserId(this Page targetPage)
{
var user = Membership.GetUser(targetPage.User.Identity.Name);
return (int)user.ProviderUserKey;
}
}

Now in a page I need to use this method in a static WebMethod, so I have added another 'extension method' to PageExtensions:

public static int GetUserId()
{
return (int)Membership.GetUser(HttpContext.Current.User.Identity.Name).ProviderUserKey;
}

and I call it as follows in my WebMethod: PageExtensions.GetUserId()