Ask An Australian

If you're going anywhere rural you have to use Telstra or their budget subsiday Boost. They have the biggest network and best coverage outside the populated areas. That said no one covers the actual outback.

Boost Prepaid 28day plans the lowest tier here has 45GB of data and unlimited calls to the United Kingdom. They have list of retailers where you can buy in store, or you can order them online. I guess you could order them to the UK but it'll sting if they don't arrive before you leave. I usually just get one sim and let my girlfriend hotspot when were away.

Hopefully that helps!

Yep definately recommend Boost! Has really good rates and data allowances.

I live here and use Boost prepaid as my main phone. You can get 365 day prepaids for $200!

I don't think you can easily get a SIM prior to travelling (unless your phone supports esim).

However, this guide provides you with info on where you can buy Sims at various incoming Aussie airports - Sydney is first on the list. Boost (as per comment from @tuff_wizard ) is in the list.

https://www.phonetravelwiz.com/buying-a-sim-card-at-sydney-airport-australia-guide/

Which cellular provider you would recommend

Telstra. They are one of the best cell providers in the world in terms of the level of service provided.

Unfortunately they make up for that by being very expensive... but you're going to spend so much time without access to wifi and fast/reliable service is worth paying for. You will get a fast connection with Telstra in places where other networks will be slow or not even work at all.

That's especially true for travelling to places like Broome. Telstra generally has good reception everywhere in Australia except for the Northern Territory (nobody has good service there... I would consider buying a satellite distress beacon if you're driving a 4WD in the Northern Territory, where simply breaking down in your car could become a life threatening situation).

Probably want about 4-8Gigs data

Telstra's base rate is 15GB for $35 (note they often have specials where you get more data... but they very rarely have a special that reduces the price), and generally the data will expire after 4 weeks.

Telstra has a bunch of plans... the cheapest ones expire after just 7 days. Make sure you buy service with a 28 day/4 week expiry!

calls within Australia

Calls within Australia will be unlimited.

probably about 3 hours of calling back to the UK

You should get five hours of "Zone 1" international calling on the $35 sim... and if you can use Facebook/Skype/Facetime/Signal/etc those will obviously be "free" (as in, use your data instead). The UK is a "Zone 1" country.

Anyone know whether it is possible to get the SIMs before we travel in the UK?

For about $2 you can buy a Telstra sim card (just a sim card, no data) from grocery stores, post offices, etc. Depending what airport you land in most likely you'll be able to buy one from a store in the airport, and they likely also sell prepaid service as well.

There will almost certainly be free wifi at the airport (and in many other places around the city) if you do need to look things up before you get a sim card.

Electronic sims aren't really a thing in Australia - at least for phones anyway. They are commonly used for tablets/watches/etc.

Using roaming is pretty cheap now. Well at least the other way around aussie going to Europe(not u anymore lol) but cant image its much worse coming here.