Can VoWifi use the internet connection over the second SIM?
Backstory: a while ago I was traveling abroad. The roaming costs are astronomical. As my ISP provides a VoIP (SIP protocol) service, I installed a SIP client app and configured it to use my ISP account. As it uses internet to communicate, I could use WLAN or the UMTS/LTE network with a local SIM in my phone (I removed my original SIM). So I could make and receive calls on my original phone number without any hassle, for low cost.
Back to today: SIP is phased out and "replaced" with VoWifi.
The question: if I am abroad, and there is no WLAN available, can I use a second (local, read: cheap) SIM (in a dual SIM phone) to connect to the internet over UMTS or LTE and use it to make and receive calls with my original phone number (using VoWifi)? Or is VoWifi strictly WLAN-only?
In other words: can I have effortless and cheap connectivity for my regular phone number abroad, like I could using SIP?