When an incoming communication is directed to a telephony device that is capable of conducting an IP-based communication via an IP telephony system and a cellular-based communication via a mobile telephony service provider, the communication is initially setup as a cellular-based communication via the mobile telephony service provider. At the same time, an IP-based communication channel is setup between the telephony device and an IP telephony system. Once the IP-based communication channel is available, the communication is transitioned from the cellular-based communication channel to the IP-based communication channel.