1. A method comprising: at a system bridge, establishing a client subscription connection with a client device; receiving an incoming communication request at the system bridge; publishing an incoming communication notification from the system bridge to the client device; receiving a client communication at the system bridge; and merging the incoming communication request into the client communication at the system bridge, wherein publishing the incoming communication notification comprises pushing a communication token from the system bridge to the client device, wherein the communication token comprises a communication identifier and a host identifier, wherein the host identifier identifies the system bridge within a distributed computing cluster comprising at least two system bridges, and wherein the method further comprises: encrypting the communication token with a key unique to the system bridge.