Hi EngModo,
Yes the discussions are great, thank you too.
When Hicom 300 came out (many moons ago) it was a follow on from the Hicom 110, 120, EMS601 etc. systems.
It was found to be 'best practice' to pre define as much as possible in every system that was to be programmed.
So for example if you went to a site or logged on to a customer site that you had never been at before you would know that a Fax Machine had a COS of 10 for example, and a digital phone with no external forwarding was COS 12 or whatever, so you had a good idea that it would work to the way you wanted it to work.
Originally COS also included the ability to dial out but that part of the COS was replaced by LCOSV and LCOSD
So you made up your tables for COS and LCOSV/LCOSD beforehand and it helped even more when text labels were introduced so you could label them up.
Originally on the older systems they used the AMO's EWADA and EWAKO but that was replaced by the COS/LCOSV/LCOSD
So if you are adding a phone then to a system you would know what default COS to add it to as it was pre defined and known to work, that then avoids problems like you came across with the DSSKEY thing.
The timer issue would be one that was popular in times past when phone calls were more expensive, nowadays most customers have installed cheaper carriers. With regard to a call lasting 5 minutes or more you could move to a Call Charging model whereby you put the bill back to the end user that made the call?