Still would like to know what permission at Greek, Turkish airport's is required in advance?
For Kerkira LGKR or Thessaloniki LGTS just as a precaution send them a day's prior notice. Except of the summer months this is not a requirement but a good practice.
For Sabiha Gokcen LTFJ contact the handling agent of the airport for more info. but again a 24hrs prior notice is the most common.
http://www.sgairport.com/