Istanbul skip the line?

I'm not sure how you can skip the line at Blue Mosque or Hagia Sophia - they are working mosques, not museums. Both open and close for about 30-40 minutes for each prayer time. Hagia Sophia has a security check which typically causes a long line to get in - lines are longest midday. I observed guides holding a place in line for people (sometimes huge groups), but that IMHO is disrespectful to the many other people who are waiting in line already.

I went to both Blue Mosque and Hagia Sophia on the morning just after the second morning prayer. There was hardly anyone at Blue Mosque and the Hagia Sophia was crowded but not as much as a return visit later in the day. Make sure to wear appropriate clothing (no shorts, no bare shoulders), headscarves for the females, and a plastic bag to carry your shoes (easier than leaving in a cubbie).

Ramadan starts on March 10 this year, which will probably affect crowds, prayer times, and restaurant service.

The Blue Mosque and Hagia Sophia don't have tickets. They are free. If you want to skip the line go either early or late.

Tickets to a mosque? Sounds very fishy to me.

Here's what I have heard about (and seen personally) on visits to Istanbul:

At the Basilica Cistern, we found long lines (though it turned out the line moved quickly, and we only had to stand in it for about 15 minutes). There was a zero-line entrance for people who had purchased online tickets (so I wondered if those who, like me, has just showed up and found a long line, couldn't one just jump online - assuming you have connectivity - and buy online tickets on the spot? Since the line was moving, I didn't try, but I might next time). There was also a zero-line entrance for people on an organized tour; there were plenty of potential "guides" standing around, shouting to people in the long line that all they needed to do to get out of that line was to hire them as their guide right then and there. We declined but saw several people take them up on that offer.

For times when there are huge lines at free/no-ticket sights, ahead of time you might pay a guide; the guide (or a helper) might get there long before you and "save a place for you" at the head of the line. You show up, exchange places with that guide/helper, and skip the line (though you might not skip getting the evil eye and a multi-generational curse upon you and all your descendants from others in line behind you...).

So there do appear to be a variety of ways once can bypass lines (the details for each, and any ethical/karmic consequences, may vary). Where there's a will (high demand, locals hustling for a few Euros, and tourists willing to pay) there's often a way.

We arrived one day to climb the Galeta Tower. Huge line. Spouse said fuggadaboudit, lets go elsewhere. I noted we could buy an (official) Istanbul Museum card right there, which included "skip the line" privileges at many attractions (though the details of that were not specified). I bit on that offer, bought us two of the Istanbul cards. Then walked over to the entrance to the tower, past the long line, and showed my new card at the door. No dice. No skip-that-line, sad trombone. We did the walk of shame back to the end of the line, my spouse glaring at me the whole time. We tried using that card at several other places in Istanbul over the next few days (including the aforementioned Basilica Cistern). Although it was a legitimate card and it covered our entry to other sites, we never got to skip a single line anywhere by showing that card. YMMV.