Not as simple as it seems
I've spoken to various admins who fell into the telecoms world due to OCS/Lync/Skype for Business.
They all thought telecoms would be a simple addition to their skill set. Boy did they learn the hard way!
Telecoms is not as simple as it seems. Plus, dealing with people like BT, VIrgin, etc. every day saps your will to live far too quickly.