Hello ​@Hilly 

Do you already have Wi-Fi Calling enabled but it doesn't work when your phone is sleepin?

What is your mobile phone? Check if there is any option in the Wi-Fi Calling settings to set up preference in Wi-Fi Calling

And thus force the cell phone to always make calls via Wi-Fi as whenever possible instead of Mobile Network. 

Sorry for a late reply, the alert to your message went straight to the bin. I do not have that option on my phone, but thank you for trying

Hello ​@Hilly 

Yes, all emails from MEO Forum are going to spam (you can create a filter to mark it as not spam)

Normally all mobile phones have this option, on Samsung it's in the phone app settings, Settings > WiFi Calling > preferred wifi

Thank you