Ng-href="tel: redirecting to call with empty number

I am using hardcode numbers then its working fine but if i am adding my angular object inside ng-href then its redirecting to call with empty number where i am doing wrong here.

Working with hard codes numbers

<a ng-href='tel:+1-800-xxx-xxx' href='unsafe:tel:+1-800-xxx-xxx'>{{Number}}</a>

Not working with angular objects

 <a ng-href='tel:+'{{Number}} href='unsafe:tel:+'{{Number}}>{{Number}}</a>

is any one have faced this issue

You should take a look at this article

Basically you have to tell angular in your config set up that it should allow tel

app.config(['$compileProvider', function($compileProvider) {
  $compileProvider.aHrefSanitizationWhitelist(/^\s*(https?|file|tel):/);
}]);

I tried your code but its redirecting with Empty number only hard codes values redirecting like first example.

Working

<a ng-href='tel:+1-800-xxx-xxx' href='unsafe:tel:+1800-999999'>Call Me</a>   

Not Working

  <a ng-href='tel:+'{{NUMBER}} href='unsafe:tel:+'{{NUMBER}} >{{NUMBER}}</a>