Number "1" on the bottom of Wi-Fi calling icon

[rev2153]

Hello,
I couldn't find anywhere what does the number "1" on the bottom of Wi-Fi calling icon mean. I'm attaching a screenshot below.
Thanks for your response!

 

[Hadron]

Do you have 2 lines or SIMs? If so it might indicate which number your WiFi calling will present as.

(Just guessing really)

 

[rev2153]

I'm using S9+ so having 2 SIMs is a possibility, but ever since I got the phone I only used one SIM slot. Also I have been using Wi-Fi calling for some time and the icon used to show up without any number. Yesterday I have noticed that the icon had the number "2" for a brief time on its bottom but then I just ignored it and today it's showing "1"