The difference between traditional telephony and Internet telephony lies in the way calls are transmitted. Instead of going via a "normal" analog or ISDN line, the Internet connection is used (Voice over IP).
There are many providers who offer VoIP solutions, enabling Internet telephony via a DSL line at very little cost or no cost at all. These providers assign you a specific number that allows you to make and receive calls on a landline.
All providers offer so-called ATAs (analog telephone adapters), which are required to connect a traditional analog telephone to a DSL modem or router.
Sounds good, but there's one problem: If you're already using a convenient PBX system with extensions, you will no longer be able to benefit from low-cost Internet telephony when calling from one of the normal extensions. And you will no longer have the switchboard features.
*Please observe the utilisation details.
... now you can have it all –
with Auerswald 
Simply the best – the Auerswald Box solution.
It combines traditional telephony and Internet telephony, providing a
simple connection between two worlds.
Thanks to the new Box you can make worldwide calls via the Internet from
any of the phones connected to your existing telephone system and the
connected terminals – even for free*. There's no need to compromise
– you can continue to enjoy your telephone's many familiar features
and ease of use.
Simply connect your Auerswald Box to the analog ATA extension and an analog extension of your PBX system. No need to change any settings to configure the Box – your Auerswald PBX system is ready to go! Other manufacturer’s phone systems are also quick and easy to connect.
And why not save money when calling from your mobile? To call from a mobile phone via your Internet connection, simply enable the Call Through function on your Auerswald PBX system.
And here's yet another highlight:
If you frequently call friends, family or your firm nearby, why not use
your Auerswald Box to link two PBX systems via an analog extension?*