Which is the best device and best type of communication for communicating confidentially on trips?

I thought I had found an optimal solution in Possio Greta:

https://www.youtube.com/watch?v=ZxZmPJUqrRI
https://www.amazon.com/Possio-Greta-Portable-GSM-Printer/dp/B002SIEM6A?SubscriptionId=AKIAJKHDPWLAVHE4KDDQ
https://gizmodo.com/235790/possio-greta-combination-printer-scanner-fax-and-cellphone

But I talked to the head office in Sweden, and it turned out that it doesn't work everywhere in the world. I can't remember the details now, but I had a lengthy discussion about it, and it's of quite limited use for me when I travel between different parts of the world and different countries.

Otherwise, is there any alternative to smartphone and internet, such as a small portable fax machine or any other device or other type of communication (analogue instead of digital etc.)? Telex, satellite, short-wave radio, SIP for fax etc.?
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hermesalphaAsked:
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RobertSystem AdminCommented:
What about using something like Skype; as it is web based all you would need is an internet connection and a mobile device such as laptop, phone or table.

You can make calls from it, transfer files etc.
Dave BaldwinFixer of ProblemsCommented:
There is NO electronic communication method that can not be intercepted.
Jeremy WeisingerSenior Network Consultant / EngineerCommented:
If you're looking for end to end encryption and strong authentication, you could use signal https://signal.org or Threema https://threema.ch/en. Using these methods would be more secure than faxing.

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hermesalphaAuthor Commented:
Thanks Jeremy, that could work. Otherwise, what about satellite telephone?
Jeremy WeisingerSenior Network Consultant / EngineerCommented:
I'm not sure how practical the attack is but there are vulnerabilities there too. http://www.zdnet.com/article/encryption-satellite-phones-unscramble-attack-research/

Best way to transmit information securely is to meet face to face naked in the middle of a large field, shielding your mouths and whispering to each other. ;-)
hermesalphaAuthor Commented:
These are two great options Jeremy, thanks! Is there any of Threema and Signal you would recommend before the other?
Jeremy WeisingerSenior Network Consultant / EngineerCommented:
Glad to help. :)

Threema would give you the strongest authentication if you exchange keys in person.
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