You interact with it every day if you use a cell phone. The control plane of the nodeb/enodeb(or "cell towers") and further into the core network in UMTS/LTE i

You interact with it every day if you use a cell phone. The control plane of the nodeb/enodeb(or "cell towers") and further into the core network in UMTS/LTE is using SCTP. Control messages for voice calls and SMS is carried a top of SCTP. Control plane interconnect between carriers for roaming is done over SCTP. (Though there's still plenty of gear still using TDM or ATM)