[refurb]

Distance over the horizon can be estimated using d = 3.57 x (h)^1/2. Distance in km, height in meters.

Width of the Taiwan Strait = 180 km (coast to coast)

Height of antenna required for direct line of sight = 2,542 m or ~8,400 ft. This would be one antenna on a tower and one on the ground.

Tallest antenna in the world is on top of the Burj Khalifa skyscraper at 2,722 ft.

If you split the difference (so each antenna just sees the other at sea level), the tower would need to be 635m tall or 2,088 ft. So if you put a Burj Khalifa tower on each coast you could make it work.

[gruez]

Or you can cross the relatively shorter distance between Shenzhen and hongkong

[jasonjei]

That's definitely much easier. Crossing Shenzhen to Hong Kong is literally getting off the Shenzhen subway, crossing a bridge, and entering Hong Kong immigration and MTR.