Hi!
I was 121 and we were on call 24/7. I was once on call for 240 hours, and then got a trip. The POI/FSDO/regional office knew all about it.
There are STILL -91 ops flying charters on -135 certifiicates, and their POIs/FSDOs know what is going on.
What is technically "legal" and what the companies can do, with the approval of the local FAA personnel, are two different things.
The -135 Duty/Rest re-write was done a number of years ago, and then shelved, because it would have cost too much money to someone....same reason the 121 Rest/Duty/Flight regs are still under review right now.
cliff
LFW