Ring groups and Queues provide flexibility.
In your original scenario, with 6 extensions involved, the caller might have had to of endured a full 120 seconds of waiting (20 seconds each). If he actually got to 106, but hung up before the full 20 second ring time, an email of a missed call would have been sent. If he waited the full time, then Vmail would be an option.
The ring group is very similar to your above in practice, but you do need the license.
In your original, a call goes to extension 100 and unless set differently for internal and external, all calls are handled in the same manner. This means that for all intents, extensions 100-105 do not have email. unless they are toggling their status to something other than available and have different call handling rules in place. With a ring group you can select the extensions you want to be a part of that group and how you want the ring strategy to be employed. In this manner, incoming calls are directed to the ring group instead of an individual ext. This preserves the ability of the extensions to have and use their own Vmail and call handling mechanisms for calls outside of the ring group - direct to an extension as an example. You can also select a ring time that is independent of what the single extension might otherwise have. In other words, it may be perfectly suitable to have a direct call to an extension ring for 20-30 seconds before going to Vmail, but you may want to cut the ring time in a ring group to something less. Your current setting of 2 minutes total elapsed possible time, is to me, way too long. Perhaps you cut the time to 10 or 15 seconds each as this still is a minute + of wait time. You also have the ability of setting the ring strategy - ring in the order in which the extension are listed (prioritized hunt), ring all extensions in the group at the same time (ring all) or page. The calls in a ring group will automatically by-pass phones that are busy so as to ensure the least amount of wait. However, this also implies a level of discipline on the part of the ring group extension owners to stay in their places or put the phone into DND or using group pickup so that phones don't needlessly ring.
The queue can be even more elegant, but will again require discipline on "agents logging in and out" so the phone system knows who can and cannot take a call. The queue also has a pool of agents as you elect and you also get to elect how they will be utilized. Depending upon the 3CX version purchased (with or without) call center module, you get even more flexibility. Calls are directed into the Q whereupon the system puts the variables that you have set as rules into action. There are more call handling options than I can go into here, but the main difference between the two (RG & Q) is that a ring group is more structured to time (goes down a line of extensions and should an extension that was busy when first contacted open up, it will not go back) whereas a Q will hold calls in suspense and try and find an agent, but gives you the rule setting capability to find the balance that best suits you and your callers' needs.
