How to check if my app is set as default calling app?

My app support ringout feature, when set Ringout, all the calls in my app will go to native, by using tel://xxx.

But when my app set as the default calling app by the user. Then when user make a call from Contact, it will jump to my app, but app will will route this call to native.

So there is a issue for this, then the quesion is:

How to check if my app is set as default calling app?

How to check if my app is set as default calling app?
 
 
Q