For future reference.
1. Can you still use a 4g Sim card in a 5G phone. For example the Samsung Galaxy S20 Ultra. Obviously that doesn't make sense as you wouldn't be able to use the 5G capabilities. But can you?
2. Is the 5g backward compatible to 4g and 3G networks.
3. What networks offer just the 5G prepaids if you purchase the phone outright? I know there are the phone with the plans.
Thanking all in advance for straight answers. I know nothing about phones.
2 Are you asking if a 5G Phone will work on 4G and 3G networks? If so, then yes.
What networks offer just the 5G prepaids
Not sure what you are asking here.
So plan only uses 5G? If that is the case I'm guessing none. 4G and 3G will always need to be a fallback given limited coverage.
3 Currently some networks require a payment to access the 5G network. I suspect they are just trying find a way to initial subsidise the cost of building the network. I highly doubt this will be the case in the future when the 5G network is fully built. i.e one plan for access to 3G, 4G and 5G.
So there are prepaid 5g plans. Assume its Telstra, Optus and Vodaphone. What about the Ozb favourites? Do they have 5G prepaid only?
Telstra: I don't know, it just says eligible plans on their website.
Optus: No, postpaid only currently.
Vodafone: Has not be launched. Planned to be launched in mid-2020
Why would you want 5G prepaid only? 5G only plans are a bad idea. 5G radio waves don't go through building very well (5G network in the future may be better at traveling through buildings) . You likely won't have good phone reception a lot of the time.
EDIT:
*Optus: I don't know, getting mixed message from Optus.
It's 25% faster service provided you are very close a 5G antennae.
Not a paradigm shifting event in world history as marketing would have it.
In Australia the 25-26GHz spectrum only goes up for auction in 2021. That is where you will see the main benefits of 5G. 5G can also operate a slightly different flavour in the lower < 6GHz spectrum occupied by 4G. A part of this spectrum has been auctioned off at around 3.6GHz for 5G but it's very limited and not the full capabiltiy of 5G so that is why the rollout is 'slow'. The future is still a way off.
Current '5G' phones don't have the support for the full 25+ GHz 'real 5G' as that is still probably at least 2 years away. (There's also talk of 60GHz devices in "5G." It will all become very confusing in the next decade with a large variety of devices being labelled as 5G.)
Like with 4G and 3G in the past, a "4G SIM" or "5G SIM" will allow the phone to fall back to whatever technology the phone and network in the area supports, but a "4G SIM" will not let you access the 5G network just like a 3G SIM won't let you access 4G.
Eventually the fallback order will be something like 5G (25GHz) -> 5G (3.6GHz) -> 4G(0.7-3.5GHz) -> 3G. At some point networks will deprecate 3G and phones will stop supporting it.