In-Network calling is basically when you are calling another VoIP phone that is directly connected to the same VoIP service provider IP network that you are connecting through.
VoIP service providers often allow you to call other customers on their network at no extra charge. This could be considered a "freemium" feature. And, why not? After all, IP routing of calls cost the VSP (VoIP Service Provider) next to nothing to route. In-network calling doesn't have to traverse the PSTN (public switched telephone network) networks to reach other subscribers on the same network. They generally route over the Internet, which is essentially free routing (when compared to PSTN routing).
The fact is, now days most VSP's promote in-network calling as a free feature on top of their paid subscriptions. But, not all do. Some want to squeeze every penny out of their customers possible.
Free in-network routing may be one of the VoIP features you may want to look for when shopping around for VSP's to subscribe to. In some respects, I think of in-network calling as a kind of VoIP Peering, only across a single network instead of across dispersed unrelated networks.
Some services initially obtain all their customers based on the freemium marketing model. For example, Skype, and Google Talk (and, Google Voice and Video Chat) obtain most of their customers based on the premise of free calling to all other Skype or Google Talk/Voice users. And, they are really providing in-network calling. It's when you upgrade to the premium paid services and place calls to PSTN and mobile phone numbers (or, international) that your calls exit the proprietary networks of Skype and Google and traverse the PSTN networks to connect to everyone else in the world, which now costs more money.
When it comes to pure-play VoIP services like Voip.ms and CallCentric, some people may wonder why it even matters to have free in-network calling? Well, consider the following:
1. You may have family in other states, provinces, or even other countries. If they too have a VoIP account with CallCentric and an ATA (analog telephone adapter), they would then be able to call you on your home VoIP phone for free from virtually anywhere in the world their ATA can register with CallCentric. And, you could call them for free, too. Talk about saving money!
2. Your business has offices in other cities, states, or countries. And, your business has an IP-PBX or various ATA's and IP-Phones at each of the remote offices. Your employees can now call anyone in any other office for free using in-network calling when all offices are interconnected using the same VSP.
Free in-network calling is one of the benefits of VoIP that is rarely encountered in the PSTN world. Why not take advantage of the savings?