magicjack plus app not reliable on iphone 4s

I have MJ plus and the official app for iphone 4s. I have wifi at home but my iphone only rings sometimes. Even with my iphone right beside the router with full signal. I of course have made sure to enable notifications and turn on sounds in my settings menu. My iphone will ring sometimes but why not every time? My wife also has an iphone and we have exactly the same random success with getting it to ring

things I have tried

1/ put mj ip in DMZ mode on router
2/ uninstall app and reinstall
3/ google search.....no answer to problem

hope someone out there has the answer......thanks

the problem may be you have to phone them first with the app. Then it seems to work when they call you back. I gave a friend my MJ iphone # and it wont ring so I called them with the app and then they called me back and my phone rang?? Give it a try may help

Absolutely !! Correct works great here.

yes I even tried that but still will only ring sometimes