I have a mixed reaction, believing part of this but not all.
For the HKPD to monitor and record all calls that go though any HK-based network is easy enough to believe. Here on the Mainland, they already do that (the only saving grace is that none of the ones monitoring the calls are very English-savvy).
As for monitoring FB, Twitter and Whatsapp... I certainly know the Beijing regime would love to do this if they could, but from my experience living here in the Jing for the past five and a half years, I'm skeptical about their ability to do so. These apps are already blocked on the Mainland, and the reason is because they refused to give the regime the power to do exactly that.
I find it odd that they would surrender that power to the HK authorities now, knowing that it will cost them a lot of customers. Now, if "monitored" simply means they've got cybersnoops who are paid to prowl around looking for posts that do not support the regime (kind of a local unit of the Wumao brigade), I can believe that.