I use Zoiper to recieve phone calls to my voip number on my android mobile and on my girlfriend's iphone.
When I make a phone call with the iphone using the usual 4G provider (Iliad), zoiper on the android rings.
When i make a phone call with the android instead, using the 4G provider, zoiper on the iphone does not ring and the line is always busy.
This makes me impossible to call my girlfriend's iphone at home when I'm out with the android...
Do I have to change something in the settings?
Any other information is requested to to solve the problem?
Thank you all for your help.