I just got the update to iodeOS 7.8, installing now.
Not sure what changed yet.
It should be beta update and only security update.
There is problem with calls for some users.
Can you confirm that calls works for you if you have already updated: https://community.iode.tech/t/cant-make-or-receive-phone-calls-7-8/8568
Yes same problem, but there is already an update to fix it I think. Mine is updating again right now, still says 7.8 but the date changed to 8/21.
I will know in a minute and update this if it still does not work.
EDIT: It is fixed in the update.
Dont get this Beta as now my notifications are all silent.
I messed up, the beta did not do this, ““I”” did. 
Not sure how but Do Not Disturb got turned on. 
I must have gotten the later beta 7.8. T-Mobile is working on my Brax3 after 7.8 Beta install
Downloaded this and making phone calls seems to be better. That was so annoying!
Still can’t make WiFi calls without having cellular present as well. This was fixed back in 6.x days but has been borked for months.
As someone who relies on WiFi calls, it pretty much renders the phone not fit for purpose.
I dont use wifi calling, but another Beta was released today might fix it.