Ask HN: How is mobile network bandwidth sharing Optus – Vodafone Australia set?

This is in regard to the new agreement for towers in rural areas. [1]

As a customer of a mobile network that uses Vodafone, there's been lots of fanfare how coverage would be better with a new agreement with Optus regarding covering more of rural Australia - however around the same time of introduction, my experience phone calls and data got worse, calls dropped out more, network less available, leaving me with a sneaking suspicion things are actually snafu or the whole agreement was a bit BS / spin.

What I'd like to know is there a level of low signal where phones prompted to use the other network, and does the phone need to be set to roam? (I've tried setting roaming but to no effect) Does it have to be a new phone, 2023 .. 2024 or newer? There's nothing I have found reading various write ups, just customers should experience better coverage.

As of now I'm sure the agreement is either not active in my area despite being rural - at the end of a frustrating day I was able to use another cellular network and found Vodafone has unexpectedly (usual on their part) decided to kill the local tower off while they upgrade it - advised only 11 days this time and at least it's not a month or more (as they have done in the past.) Optus's mobile network is working just fine - however there's no sharing of their coverage with Vodafone network resellers.

This begs the question, when does this sharing come into effect, is it based on signal strength or only if the respective network doesn't have their own tower in the expected coverage area? In other words is if both Optus and Vodafone have towers a few miles / km apart is that considered the same coverage area and thus outside the agreement, with it only in force when towers are many miles / km apart?

Another thing I'd like to know is how many other people in Australia using either Vodafone or its network resellers, have noticed a decline as well which would match the start of this network sharing agreement?

[1] https://announcements.asx.com.au/asxpdf/20240429/pdf/062ymhk13r4lpg.pdf [pdf]