Wideband audio is commonly used today in VoIP environment. Some vendors call that "HD telephony".
Only view people know that this was possible since the end of the 80ies in ISDN environment by using G.722 codec.
I wanted to support this within Phoner when using ISDN/CAPI mode. The problem is to find a compatible peer. Normally a special type of service is set, but you won't find a compatible destination for this, therefore after some seconds a "normal" call will be established. Therefore I am using the way the vendor AVM uses to "mark" such calls by using a special LLC (Low Layer Combatibility).
What is working at the moment:

• A direct call between two Phoner instances over the public ISDN network.
• A call between Phoner attached at the internal S0 port of an AVM Fritzbox and a SIP extension using G.722 codec.
• A call between Phoner attached at the internal S0 port of an AVM Fritzbox and a HD-DECT device at this Fritzbox.
• A call between Phoner attached at the internal S0 port of an AVM Fritzbox and another Phoner instance or a Fritzbox behind the public ISDN network.
• maybe there are other scenarios too, but I didn't test that.

What do you need to test that?

• Phoner in ISDN/CAPI mode from version 2.51
• I tested with ISDN card Fritz!PCI from AVM, but other ISDN hardware should work too.
• Enabled option "Wideband" in Phoner at "Options/Communications/CAPI".
• A samplingrate with at last 16000 Hz (16 kHz) should be configured at "Options/Sound"
• Usage of a high quality microphone supporting high frequencies (7 kHz and above). You would hear any difference if you are using a poor microphone that cut high frequencies.