This morning I upgraded my iphone 5c to IOS 9.0.2 using my G5 10.6.8 and itunes 11.4. No warnings of incompatibilites from itunes of course. After upgrading the phone is no longer compatible with itunes 11.4 as we now know.
"The iphone cannot be used because it requires a newer version of iTunes..."
There is no itunes upgrade beyond 11.4 available for Mac OS 10.6.8
There is no system upgrade beyond 10.6.8 for old machines (or maybe you have lots of 10.6.8 dependent software hardware)
There is no way of reverting back to IOS 8.41 on the phone as Apple have stopped signing that version a few days back.
I talked to three levels of Apple support who all tried hard to find a solution but confirmed that there was no way to fix the problem. They did acknowledge that itunes 11.4 should not allow a fatal upgrade like this without some kind of warning.
I can see no way out of this problem with out new hardware, mac OS, itunes etc unless someone smarter than me hacks an IOS downgrade process.
Very very frustrated to have been stupid enough to accept an upgrade.
phil