Regular warning:
Beware of audio or video calls via @signalapp if your #mobile phone #tariff is #metered (i.e., you have a monthly etc. traffic quota).
Signal eats up your mobile quota even when you're literally sitting next to your internet router and your WiFi connection is perfect.
The corresponding issue has been open for more than than 6 years.
It has also been discussed in the forum, with many users tuning in and confirming the issue.
There has even been a pull request for a solution. It has been closed due to "inactivity", with no Signal team member even bothering to reply.
You can of course turn off mobile data when you're about to make a call, or when you're being called. Unless you forget to, in which case your money will go down the drain.
#Signal