//The native wrapper:

static int ast_mono_wrapper_ast_cli_command(int fd, MonoString * s)
{
	char *s_charptr = mono_string_to_utf8(s);
	int retval = ast_cli_command(fd, s_charptr);
	g_free(s_charptr); // PASSBYREF? -- FREEIT?
	return retval;
}

// The wireup
mono_add_internal_call("Telefinity.ManagedAsterisk.Core.Cli.Native::ast_cli_command", ast_mono_wrapper_ast_cli_command);

// In my Cli.Native.cs class:
[MethodImplAttribute(MethodImplOptions.InternalCall)]
internal extern static int ast_cli_command(int fd, string s);

// And then as part  of the Cli object:
public int Command(int fd, string s)
{
    return Cli.Native.ast_cli_command(fd, s);
}