The 2.5 mm jack is going well in the socket of the Siemens device and then you can start actually already.
I was very surprised by the excellent voice and audio quality. Sounds even better than to work directly with the listener at ear for me. Register my caller me, can they "call normal" against the notice no difference.
The headset is now since about 3 weeks in my possession and I am very satisfied. I can not say anything yet, but I think, if used properly there should be no problems over the long-term durability.
For the price this is fully okay and is recommended.