If you would like your WebRTC endpoints to communicate with each other (voice, video, messaging, data) in addition to being able to call the PSTN, this consideration actually brings us back to signaling. Choosing a SIP signaling platform is likely your best option here because it works well for both peer-to-peer scenarios and endpoint-to-PSTN scenarios. SIP has become the de facto standard for VoIP, and the majority of VoIP systems have integrated with the PSTN.
Challenge: In networking scenarios involving firewalls and NATs, servers are often needed to facilitate WebRTC connections.
Lastly, while WebRTC aims to create true peer-to-peer media and data streaming once a session is established, the reality is that most devices today live behind one or more layers of NAT, and many are behind corporate firewalls. WebRTC apps use a framework called ICE to successfully overcome the complexities of real-world networking in most cases. But, there are a non-trivial number of cases where ICE cannot succeed to create true peer-to-peer media connections. In these cases, ICE relies on the availability of media relay servers (TURN servers) in the cloud, on which it can fall back to relay data between endpoints.
Conceptually, media relay servers have the simple task of relaying a stream. Media relay servers have public addresses, so they can be contacted by peers even if the peers are behind firewalls or proxies. It's important to note that media relays require reliable congestion-free Internet connectivity to effectively operate. Poorly operated media relay servers can introduce quality issues such as choppy media and disconnected sessions. Based on their bandwidth requirements, media relays can be rather costly to operate.
Tackling media relays is, like signaling, a hefty task, but it is necessary to enable WebRTC applications to perform to enterprise-level standards. You can choose to operate a media relay solution or find a hosted solution. If you are selecting a hosted signaling solution, be sure to investigate whether they handle media relaying and, if so, how they ensure QoS.
With the right approach, you can take advantage of the disruptive business opportunities WebRTC promises today.