1. FreePBX
2. findmefollow
3. source strings
4. review

ring first extension in the list, then ring the 1st and 2nd extension, then ring 1st 2nd and 3rd extension in the list.... etc.

ring first extension in the list, then ring the 1st and 2nd extension, then ring 1st 2nd and 3rd extension in the list.... etc. This strategy will work only when Confirm Calls is disabled.