There is a conference phone network hosted by eventphone. The most popular way to access it is indeed using DECT handsets, but you can also access it via SIP (p

There is a conference phone network hosted by eventphone. The most popular way to access it is indeed using DECT handsets, but you can also access it via SIP (probably the second most popular method), GSM (yes, really, they used to hand out SIM cards), landline (supports rotary phones!) and probably even more esoteric ways. There's also a post office delivering mail both internally and externally.