One problem ....
Hunt Groups work very much like a call center queue.
The Hunt Group monitors your hook switch status.
If your off hook (on a call) the hunt group will not deliver a call to you and there is no way for you to tell there is a call in the hunt group queue. Hunt Groups are often referred to as "Poor Man's ACD".
Here's an easier solution.
Extend the forward no answer delay on your telephone.
Sounds like your currently at 4 rings, try setting it out to 6 or 8 to give you more time to grab the 2nd incoming call.
You can also setup a feature in your mailbox called "Call Display". This feature will play an alert tone on your set when a call rolls over to your voicemail box. The alert tone is played to get you to look at the display. The display will show you the caller ID of the call that rolled to VM. At this point you have the option to let the caller leave a message or to interrupt VM and pull the call back ... kind of like picking up your home phone when you hear somebody leaving a message on your answering machine.
Here are the steps for Call Display.
Press Feature 981 to open mailbox.
Enter your mailbox password and press OK or #.
Press ADMIN or 8.
Press GREET or 2.
Press CFWD or 3.
Press NEXT or #
Press CHNG or 1 to turn Call Display on/off.
Press Rls
Feature 987 is used to interrupt Voice Mail when a caller is listening to your personal mailbox greeting or leaving a message. This allows you to pull the call out of Voicemail and speak with a caller who has reached your mailbox.
HTH!
-SD-