I have Optus HFC NBN, and about every week or two (twice this week already), it goes down for at least a couple of hours (2.5 days once!)
I want to implement some kind of backup internet, and 4G is the only real option.
I can't use my phone because I'm not always there when the internet goes down.
What I'm ideally looking for is a prepaid data-only SIM card with long expiry, or with the ability to buy data blocks as and when I need them. Does anyone have any ideas?
What are your signal levels for your HFC? It sounds like that needs to be addressed. My Telstra HFC needs frequent servicing (once every say 9-12 months) as the tap in the street corrodes. Until it gets fixed the problem will persist, and probably will get worse.
Otherwise, if you really want 4G backup, Vodafone frequently offers 6 month expiry data SIMs with a fair bit of data for very cheap (about $25). I would use those.