I thought you guys might be interested from the perspective of someone who's actually working on these islands in the SCS:
One of my brother in law is a senior engineer with China Mobile, and he's been sent on a one month 'deployment' to the islands in the Paracels. His is tasked with the supervision of building communication networks and their maintenance. I've been following his blog on WeChat
He says almost all of the inhabited islands in the Paracels now have full 4G coverage and is connected with undersea fiber optics to the mainland in Hainan (mainly for military use).
He says the airport at Sansha (Woody Island) is the busiest with military fighters it has ever been (just in today) - and he's been to the island a few times. There is a heavy presence of major construction firms, military personnel and surprisingly TV crews. He would gladly take photos but apparently the whole island is littered with surveillance cameras he's afraid to get caught.
He also complains about the length of his trip because he won't be able to see his newborn daughter for a month, and that conditions are tough! They eat all sorts of weird tropical fish the fishermen catch in the surrounding waters, and things like no fresh-water showers and drinking water of questionable quality (he jokes about being told coloured 'natural water' is good for health) are amongst the elements they face.
It looks like China is serious about stepping up presence in the SCS and they are increasing the pace of infrastructure building to support it. Anyway I hope I haven't bored you guys with these stories