Hi Robber80.
Two comments about your interesting post:
After reading some of these posts and seeing how few people are on here complain about this problem, its rather obvious to me that not all phones are acting up.
The point is that a vast majority doesn't call through their iphone. And even people that call from time to time will have a 1-2 seconds lag that is considered almost normal. This thread wouldn't exist for that mini lag.
I'll give you an example. When I realized this nasty bug, a workmate (6s too) swore to me that he never never had had this bug. Some weeks later, this call connection was found: I took his phone, took mine, and performed our test. 10 calls. And guess what? There was a lag in both iphones!!!! The same 5 seconds lag. He was amazed...
As he barely used his iphone to call, he had never realized in 6 months that it existed (and actually he has forgotten 😟)
My wife phone does NOT do this at all on both iPhone 6s or 7.
If this is true it could be an important clue. I'd appreciate if you could do a more controlled test:
1) Take both iphones, yours and your wife's.
2) Do the test at the same time. (open camera at both devices, call N times, then reopen camera at both iphones)
3) Compare the lag result.
If you find that there is a significant difference (for example, 6 seconds against 2) please post it as soon as possible!!!!
It could be a chance to figure out how to mitigate it.
Some of the people in this thread (and also myself) have tried any conceivable configuration possible with no success (clean install and only native apps, no restoring, disabling icloud, disabling live photos, disabling mobile data, disabling wifi and so on...). But maybe there is some missing point and your wife's configuration could help.
If the lag is the same, we'll have to wait. Again...
By the way, has anyone tested this in iOs 10.1 beta???