Well, without addressing any specific system or systems, as nobody can conclusively give you a best/optimal route as there is no such thing covering all bases and broken comma scenarios -
- Outside of telecoms (copper, fibre, ground-sat and sat-sat linked/networked gateways) based network distributed ‘telephony’ digital or otherwise, you won’t find a robust cross-nation alternative, not even a cellular based one as even cellular systems use some degree of land cabled backbones as well as wireless backbones to network the cell sites to each other and link/gateway into other non-cellular services.
Probably the closest you’ll get is maybe one of the sat networks that are primarily sat-sat relayed and networked, but that’s only assuming all parties involved use sat phone type equipment or voice-over-data (VoIP equiv outside of the internet regulars) via sat link equipped terminals.
I believe some cellular networks have the capability to retain cell-cell relay within the same network in the scope of limits that only active cells will be available, but I couldn’t quote a specific that I know had the fallback live available.
So that leaves us with simplex and repeater based radiotelephony non-cell based. Outside of commercial systems that licensing usually excludes repeater and gateway operations under the lowest paid licensed and license-free/exempt tiers, you’ll be looking at simplex only systems. In other words, station to station direct and with the usual range and degrees of LOS based range potential and reality.
So given that bit of cold reality, you are looking at which ‘system’ is both highly active normally, so ensuring that range/conditions permitting you’ll have the best chance of getting contacts to directly exchange info or get to relay for you.
If you are looking at emergency only standby and already have links/association with a comms network using a common system, then you’ll want to pretty much clone the lowest common denominator of their preferred setup or better.
If you are organising your own, think about availability and range and decide if you need a closed or publicly available system, as each has their own advantaged and limitations, but a publicly available system should be of readily accessible kit and frankly idiot proof to setup and operate/navigate.
Now as a rule of thumb, lower frequency range systems (longer wavelength) have better scope for range and more scope for extended range where upper atmosphere conditions aid EM propagation, but at the same time, optimal antenna systems can get quite bulky when you’re talking under 70mhz territory. I chose 70mhz as, based on UK (where I am), this was the VHF low-band land mobile radio territory.
When you get into 30-70 MHz territory, you’ll be pretty much looking at 49mhz restricted power ops or (if ham licensed, additional 6m ops 50-52mhz territory). Assuming non-Ham use, it’ll be 49mhz (analogue only where we’re talking ISM type license exempt use) and usually handheld equipment territory and usually without legal usage of external antennas and linear RF amplifiers, so talking (depending on region) double figures in mW operating power based case typically and fairly LOS operation within the associated range limits allowed by such low power ops at the frequencies in question. I did some good stuff on 49mhz under such limits as a kid, so it’s not beyond scope for inclusion but not high on the high availability list of options.
So unless you’re wanting to venture into ham radio ops (where there’s an unbelievable scope for long range ops due to many operation modes allowed and many frequency range to play with), you’re really looking at CB under whichever licence grade your country permits SSB usage on 27mhz, as the ‘long range’ option (not available here in the UK as it’s strictly FM only in our 11m CB allocation) that’s also readily accessible via ‘export model’ equipment more readily.
At 11m/27mhz, you’ve limited degrees of extended range due to propagation associated with HF operations, but most of the scope never is usable upwards of 21mhz where 21-30mhz straddles the borders of both VHF propagation at the higher frequencies and low grade HF propagation at the lower extreme of that range.
So, having got legacy analogue dealt with, modern digital and analogue ‘commercial’ and commercial derived systems are well into VHF/UHF territory, I’ll skip SHF stuff as SHF is dark magic territory to most and unless you are ready to venture into dark magic technicalities, beyond most people’s scope for patience to explore.
So that, assuming VHF/UHF ops, brings you back to the systems you mentioned and back to my advice about deciding if you need high availability public comms or a more closed group system. There maybe some repeaters used on some commercial/semi-commercial leisure systems that allow repeater use or have unlicensed operational availability for, ditto for trunked/linked inter-repeater cross linking, but the systems I’m familiar with don’t permit such fancy operation modes at license-free/exempt and loftier at-cost licensed levels.
So at that, I’ll hand this back to anyone who wants to add/revise this based on US/Canada based usage and scope and likewise for other regions, as the initial subject has scope for being investigated worldwide.
But the bottom line is - you won’t find anything remotely close to internet-backboned or land cabled backbone based radio relay systems in the more regular LMR systems if the internet craps out and/or the landlines die a copper death.
That’s one of the reasons I value my ham license, because whilst HF operations won’t replace regular telephony systems, I know there will always be contacts occasionally even if the world goes mostly dark 