I have sip phones and land line phones in one ring group. I also checked “skip busy agent”. I set call waiting for all extensions in my freePBX.
For my sip phone, I set “line key 5” to “extension 6” which means that Key 5 shares the same extension of Key 6. So, when Key6 is on the call, 2nd call to key6 will arrive on key5. This work well when the 2nd call is coming directly to that extension on key6. However, a 2nd call will not arrive on key5 if the call is from the ring group where “skip busy agent” is on.
It maybe my misunderstanding that since I have call waiting on for my sip phonea, I thought my sip phone will never go busy with just one call. However, this experience leads me to believe that ring group treats call waiting differently, under the condition of “skip busy agent”.