A scenario
Larry (VT l1) calls DN 777
This rings VT c1 and VT e2
Later moe joins the call by bridging
- By picking up m3, which was reserved by the 1st call
curley on VT c2 calls 8888
- Ringing m1 and e3 (and a tone generator)
- While ringing, curley invokes a conference, merging the calls and dropping c2