Dual sim problem

[kaiak]

Hi there :
I use dual sims on my 7T. from different carriers.

SIM1 only for voice call and on 3G network (in my place 3G has better signal than 4G)
SIM2 for DATA and on 4G .

when i do voice call by using SIM1, Sim2 drop to 3G and slow speed.(showing H or H+ on top bar. )

as in Australia non-carrier support VOLTE or VOWIFI on Oneplus 7T (or say all the oneplus phone base on my research),I can understand when voice call the network have to switch to 3G from 4G then go back after calls.
but in Dual Sim setup ,is it should be remain the network type and has same fast speed ?

Thanks in advance.

 

[ziddey]

There's only one modem, so it can only do DSDS (dual sim, dual standby). When in a call, the other connection is dropped. This is why your data switches to sim1's 3G.

Are you intentionally trying to avoid using volte/vowifi for calls? If not, you likely need to do this: https://forum.xda-developers.com/oneplus-7t/how-to/volte-op7t-t4007085

 

[kaiak]

There's only one modem, so it can only do DSDS (dual sim, dual standby). When in a call, the other connection is dropped. This is why your data switches to sim1's 3G.

Are you intentionally trying to avoid using volte/vowifi for calls? If not, you likely need to do this: https://forum.xda-developers.com/oneplus-7t/how-to/volte-op7t-t4007085

Hi Thanks for your reply.
I see the reason. so DSDS can not support the way I want to use.
I tried the link you mentioned before. no luck.
In Australia, oneplus is not officially on market. So none of carrier support Volte on Oneplus.
My understanding is VoLTE and VOWIFI have to be supported by Carrier AND the Phone.
My oneplus 7T can open and use VOLTE when traveling overseas if I use local sim.
Our local forum have discuss this issue long time. No solution so far.

Some other phone like xiaomi or so can be supported in Australia. I was wonder why oneplus not.
Flash other country's rom may be ? Is there have a Volte international roaming thing ? So 7T can be pretended a Euro device roaming to Australia and using Volte ?