my connection to voip.ms was pretty good last week; however it drops often, even when I have subscribed to the push notifications. Today dropped twice and it is just mid morning here in toronto, canada.
The only way to get it back working on my iphone 6 is to go to settings (in zoiper); incoming calls; uncheck "use push notifications", and then recheck the same.
I then get the nice green "ready" notification when I got to the zoiper dialpad.