Hi everyone, I know there are already many cases here, but still want to share mine and check whether there could be any chance I can get it fixed.

My phone is a HONOR phone China version. I’m currently in Australia and have 3 SIMs:

 

1. amaysim Australia SIM
2. 2degrees New Zealand SIM
3. China Mobile SIM

The amaysim SIM and China Mobile SIM work normally in Australia. It can use 4G/5G data, make and receive calls, and VoLTE works properly for both SIM.

However, my 2degrees NZ SIM can connect to 4G/5G data while roaming in Australia, but it cannot make or receive voice calls. I have manually selected both Optus and Telstra (Vodafone doesn't accept my registration). Data works on both networks, but voice calls fail. The phone shows IMS not registered for the 2degrees SIM, and VoLTE does not appear for that SIM.

This same HONOR phone has previously worked normally with:

 

• amaysim in Australia, including VoLTE
• Chinese SIM cards roaming in Australia, including VoLTE
• 2degrees in New Zealand, including VoLTE
• amaysim roaming in New Zealand, including VoLTE
• Chinese SIM roaming in New Zealand, including VoLTE

So everything works fine in NZ and China.

The issue only happens when the 2degrees SIM is roaming in Australia. In Australia, the same phone and same SIM can use 4G/5G data, but IMS does not register and voice calls do not work.

I have tried the following:

 

• Swapping the SIM cards between SIM slots
• Disabling the amaysim SIM and only using 2degrees
• Using only the 2degrees SIM in the phone
• Manually selecting Optus
• Manually selecting Telstra
• Replacing the 2degrees SIM card with a new SIM
• Restarting the phone
• Toggling airplane mode
• Disabling 5G and using 4G/LTE only
• Enabling and disabling VoLTE, VoNR and Vo5G-related settings
• Using Shizuku + Pixel IMS to expose hidden IMS settings
• Enabling VoLTE / VoNR / Vo5G-related options in Pixel IMS
• Trying options such as carrier_volte_provisioning_required_bool, carrier_volte_show_switch_bool, and other related carrier config settings suggested by ChatGPT

The result is still the same:

2degrees roaming data works in Australia, but IMS is not registered and voice calls do not work.

I have used this phone only for a year, and not really the ideal time changing for an iphone. Any advice from people familiar with IMS, VoLTE roaming, Pixel IMS, carrier config or MBN profiles would be greatly appreciated. Thank you guys.