//引用单元：FMX.PlatForm, FMX.PhoneDialer
procedure TForm1.Call(ANum: String);
var
  PhoneDialerService: IFMXPhoneDialerService;
begin

  if TPlatformServices.Current.SupportsPlatformService(IFMXPhoneDialerService,
    IInterface(PhoneDialerService)) then
    if ANum <> '' then
      PhoneDialerService.Call(ANum);

end;
    这里使用的SupportsPlatFormService会返回PhoneDialerService实例！