Headband and charging station are included.

I use it in parallel with a Mitel 612 system telephone on an OpenCom 510. It works perfectly.

I have paired the C565 with a Gigaset A415. Calls from outside work very well. However, when I call someone, I have to do it via the phone (mobile station) and then transfer the call to the headset. I don't find that practical.

No, it can only be connected to a DECT phone via the DECT function. Over-Head is not included here.

According to our enquiry, this headset is unfortunately not compatible, as the Aastra does not have a DECT function according to our information. We recommend headsets of this type for the Aastra https://www.digitec.ch/de/s1/producttype/office-headset-459?tagIds=77-733&pdo=1049-3009%3A1110&p=1512%3A225994 , as these can be connected to the telephone by cable.

Pairing with the Gygset 400A base station worked, but it was a bit of a tinkering and I can no longer understand it. All I know now is that I have to dial the number first and then press the pick-up button twice so that the headset takes over the pairing.

Plantronics C 565 GAP is not a wireless phone, so it is not possible to establish a wireless connection. A physical connection from the charging station is not possible. The C 565 is connected to the DECT base station like any other DECT handset.