I am curious about the headset which have button to accept call or reject the call. Can I just buy such headset and connect it to my telephone? I mean would it work or do i need to buy special telephone or are there any additional things I need to buy, connect?
I think the question(s) are not possible to answer without detailing the phone in question, and may be better answered by your doing a bit of Googling. Does the manufacturer have accessories, so you can be sure the headset is compatible? I would guess that it may depend on whether it is an audio jack or a USB connector, but have no idea.
In the UK most telephone headsets I have used have a plug on that fits the phone - most phones that accept headsets have the same socket so the headset can be used on them all.
However, you are talking about accept/deny buttons - I am unaware of these being on the headset so as above- I'd do some searching, ask the headset supplier etc. about it and your phone.