We're currently down in the lowest part of the solar cycle (e.g. very few sunspots) which has a great influence on skywave propagation.
When there are a lot of sunspots, you will be able to make contacts in modes like Olivia (and nowadays FT8) but also classic Morse code across continents pretty much every day if you pick the right frequency on the shortwave bands. The throughput is relatively low, but in Amateur Radio the "journey is the reward", so it's more about making contacts, testing what is possible etc. rather than exchanging a lot of information.
With the current low sun activity, the skywave propagation is a lot worse, but even now you will be able to make contacts across continents pretty much every day, especially on the 14 MHz band (20m), even with power as low as 1W and simple antennas (like a full size dipole). The "windows" when propagation between two places on the planet is possible are much shorter though.
You can experience this in real time by observing the beacon transmitters of the NCDXF International Beacon Project, which transmit in fixed timeslots on various frequencies, with beacon locations around the world.
There are web-sdr receivers where you can listen to the shortwave bands in real-time from your browser (http://websdr.org/ for an extensive list) and if you tune one of them to 14100 kHz (CW mode), you will - over the 5 minute cycle that it takes for all beacons to transmit - receive a number of the NCDXF beacons. To identify which one was transmitting without learning Morse code, refer to the chart at https://www.ncdxf.org/beacon/.
The beacons transmit their callsign followed by four long dashes at 100W, 10W, 1W and 100mW transmitter power.
Try this at different times to see how band conditions change; they do a lot over the course of the day!
I could go on and on, shortwave propagation is one of the most fascinating things, isn't it? :-)
For phone (aka voice audio) you can have some success with 100 watts and a simple dipole antenna. You'll be better off using an antenna with more gain and/or transmitting more power, though. The highest power ham radio operators can use on HF is 1500 watts, but this requires a significant investment in amplifiers etc.
Well... If FT8 is considered normal these days then 1 watt is maybe 2-5x too high of power if you have a nice antenna and favorable conditions for intercontinental short text messages.
Absolutely with a good antenna! It is super super slow as far and transferring text data goes. I can type faster in many cases. At 10W with a good antenna I'm booming the airwaves with my signal! I've made contacts all over the place using Olivia and it's lots of fun. Get a General Amateur radio license (US FCC) and get on the air! There are regular meetings that does this if you want to listen in: http://idigit4u.com/ccara/digitalmodes.html
It is a shame that SMS and other low MTU packets aren't transmitted over a low bandwidth channel, or at least as a failover option. SMS coverage would be doubled in range, at least.
When you consider fiber as just a very narrow RF waveguide (ever seen or held in your hands a 120GHz band radar waveguide?), frequencies in the terahertz make absolute logical sense.
I know that's not a lot of power but can anyone provide comparisons to "normal" communications intercontinental?