Always or Just Once?

Have you ever got a new phone and in a week, you can't  make calls?  Well, I was faced with this situation yesterday afternoon and I kept thinking "Why me?  Why my phone".
            The last call I was able to place was through Viber.  After that, I could not make any regular calls.  I would press the call icon and then a blank screen would emerge and vanish like a typical bug. I tried it on different people ( as though that would be the issue!).  Nothing.  No indication of a call. I didn't like the look of it. I checked online and there were various solutions like get a new SIM card, change Wi-fi settings and I tried all that as well.  All to no avail.  Would I have to take my phone to a mobile shop?  In between all this, it did occur to me that something had happened when I used Viber.  I had given the option Always instead of Just Once just before the call was placed in a dreamy haze.  Now I really did not know how to undo that.  So I uninstalled Viber and tried to make a call and voila, me phone was back to normal!!  And then I re - installed Viber and it still worked.  Only this time, I gave the option as Just Once.
 Now these are options, do you want to always place the call using Viber or do you want to make a call with it just once?
  Because when you give the option Always, the default app settings change.  And this is what happened to my phone.  So I could not make calls using the regular mode.  Now if you know how to change the default settings without uninstalling Viber, that's fine.  Otherwise just uninstall, place a regular call and then re-install.  And make sure you set the option to Just Once when you use Viber!!