I posted my frustration about the difficulties of using the vouchers, a few week back, but yesterday I had a very good experience; I stopped by the TK office here in Saigon and after 10 min. I got an upgrade for SGN-BKK-IST-OSL later this month. One voucher for all segments. I have gotten the exact same upgrade once before, also that through the TK office in Saigon. Guess its better to keep a personal relationship with the staff there, than trying to call the TK CS in Istanbul to upgrade :-)