Suppose you have a lots of funding and access to all the technology available in the free world. You also have political connection & persuasion, to get your hands on any of it, whether civilian or military.
Is it possible to build a system of satellite chat phones which would allow you to communicate via text messages everywhere in the world.
Something like Viber / What's App, with only text messages, where people all over the world could buy the phone, buy subscription, and communicate everywhere in the world via texting each other?
The phones don't have to be handheld, suitcase sized phone would do as long as its portable.
The communication must be two sided, like two way pagers example Motorola 900
Any year in the 80's would do before 1989.
Please ignore Challenger disaster as a possible bottleneck for launching the constellation of satellites.
Also ignore all the governmental permits, like ITAR, assume that you will get any license you need, and all the launching slots you require.