Is there call control when using RJ 45-2.5 mm audio with DECT headsets?

Short answer:

When using the RJ45 – 2.5mm audio cable with DECT headsets, there is no call control / EHS capability.

Long answer:

Enabling Auto link can give remote call answering possibility

The auto link function can be enabled for the headset to work, which is done by moving the fourth DIP into the lowered position. This means that an active connection is established between the headset and the base station whenever the headset is taken out of the cradle. A successful connection can be seen by the blue LED on the base station.

Does the call control button on the headset end a call?

Using the call control button on the headset will connect the headset to the base station. Pressing that ends the connection between headset and base station, the call itself does not end, there is simply no longer an audio signal being sent to the headset. By pressing the call control button on the headset the audio link is re-established.