Open jaw using miles?
 

This is an area I've never ventured. Looking at a cruise that originates in Istanbul and ends in Athens. If possible I'd like to use miles. If this not allowed, any suggestions?

An open jaw is allowed if the unflown segment is shorter than either of the two flown legs. Assuming you're flying from the USA (not Budapest) this kind of ticket is allowed.

I have two open-jaw award reservations in my account, and they are an amazing value. Believe the "you can use $x instead of miles" had the value coming out to $0.10/rdm.

We have a similar open jaw (WBC, 100K miles each) next fall -- out to IST, back from TXL. In between, we are flying IST-MUC-WAW-MUC-VIE on LH and then taking a train to Berlin.

Your plan should work just fine. Be sure to allow at least one full extra day before & after the cruise.

Sure, this is fine.
 

Doesn't matter whether it's miles or money.

I just did an open-jaw FCO-EBB-FRA (yes, there were a couple changes along the way, why do you ask? ;) last month, inserted into a previously booked trip as a replacement for the return half of a cheap LH FRA-FCO RT.

Be advised you can have only one open jaw per itinerary. If you fly into IST and out from ATH, you must be starting and ending your travels in the same US city.

This is an important point, good of orlandoplat to raise it. And of course when you're burning miles, you do want to keep everything to one itinerary if possible. (When paying, long intercontinental trips sometimes come out cheaper if broken up into pieces - it's not at all uncommon for me to show up at the airport with 3 or 4 itineraries stapled together and ask if I can check my bag through. ;)

Rules change but I have used an open jaw or a stopover but not both on the same trip.

Open jaw are a nice way to see 2 cities in Europe and potentially save some money. They can be used elsewhere, too but aren't as useful in Asia because of the distances between cities.