VOIP USB phone call to ATA/router combo possible?

Is is possible for a user with a USB voip phone (plugged in a PC) to place a call to someone using a ATA (sipura) connected to a router?

Is the reverse possible (ATA call to USB voip phone)?

Thanks!

It *can* be that simple, but it rarely is..! Usually, you register with one of the many VoIP providers, who allocate you a phone number that can be dialled from anywhere, including the PSTN. Depending on the provider, it can be free or more usually a small monthly charge. Calls to other users on the same system and others that have a peering agreement are free, calls to the PSTN are charged, but are almost always cheaper than using a POTS phone.

Ivor

I don't know enough about the basic architecture to make an informed decision. Is it just a matter of dialing the ip of one phone from the other? Thanks.