Is it allow to advertise my 'iPhone-app-itunes-url' with google adwords or Facebook ads?

Yes, Google allows to use mobile app URL directly in ad copy. Instead, I would recommend you to create an app specific landing page and using that page in paid campaigns. From there, you can allow visitors to explore the app in iTunes/Web interface. Here are few best app landing page designs you would like to see. http://leafletapp.com/ https://www.dropbox.com/iphoneapp http://ambianceapp.com/iphone# http://billminderapp.com/ http://www.jiwire.com/iphone http://typographyapp.com/ http://airphonesapp.com/ http://notaapp.com/ Hope this helps!

Yes, even before the aforementioned ad extension, you could advertise any URL you like.  In some instances, you would have had to submit for Google to re-evaluate your submission, but they usually go through at least on the second try.