back in the day
Mid/late 80's . I was working with a public body/nationalised industry, replacing their ageing strowger pabx's with digital boxes. On the Strowgers not many people had "level 9" access (for direct dialled outside lines) which created quite a workload as legitimate calls from everyone else had to go through our own operator(s) to be dialled and connected manually.
The bills for the outside lines were all itemised (by BT and Mercury) , but on the strowgers there was no way of attributing those to individual extensions. It was also very difficult (aka neigh on impossible) to block any particular outside number from those who did have legitimate level 9 access. Some of the numbers called and costs were quite eye opening as the fledgling premium rate service industry was going through quite an exponential growth. I think the most popular numbers of all were horse racing and bookie numbers run by some of the national newspapers..... I seem to recall the single most expensive call we logged was around £120, which was about an annual bills worth for most people back then.
So, on the new digital pbx's we were running call logging software on all extensions, and gave level-9 to a whole load of new extensions, letting them know that calls were being logged. (which saved a lot of operator workload and thus quicker response) We of course put blocks on all the dodgy 0898 and similar numbers, but we could now see who was attempting to call them. The folks who now had level 9 access for the first time were generally very responsible, but some of the existing level-9 holders.... Well, It was rather eye opening as we could bypass the block and hear what some individual senior managers had been calling during working hours. Oh dear - you would probably not want to share the lavatory with them afterwards.
Of course, installing the new PBX's was a weekend job, and normally a Saturday night one as the organisation was effectively 24/7, which meant we had to test all the various levels of blocks to make sure they all worked from all classes of extension, which occasionally required entering the wood panelled offices of the bigwigs and making calls from their phones to dodgy numbers with and without the blocks in place. Some of the bigwigs had "mini pbx's" with manager/secretary and conference facilities that ran outside of the PBX often with unusual setups so not always easy to simulate by jumping in on the krone frame.
One of the other interesting aspects was that all extensions could make 999 calls, but would normally get rerouted to our own operator so that they were aware of the emergency and could co-ordinate things properly rather than an individual person calling the public emergency operator from our switchboard number which would not have given a very accurate user location. Only if our own operator could not answer would the call go through direct to the external 999 service. 999 calls would take priority over other calls in progress (ie someone would get dumped if all lines were busy) Which all had to be thoroughly tested. Turns out that at 4am on a boring sunday morning in some small provincial towns the 999 operators are rather welcoming of friendly calls from telephone engineers and enjoy a quick chat about things as we place multiple calls at the same time to try and make things fall over.
Happy days and a great learning experience for a student.