In order to open URL using the corresponding system application you need the whitelist plugin. If your project is based on the scaffolded demo program, it should already be installed. If not (or simply to ensure that) :
ionic plugin add cordova-plugin-whitelist
Once the plug-in is installed, you will have to specify the intend you want to open from your application. In your config.xml, add:
<allow-intent href="http://*/*" />
<allow-intent href="https://*/*" />
<allow-intent href="tel:*" />
<allow-intent href="sms:*" />
<allow-intent href="mailto:*" />
...
Given the above rules, all URI stating with one of the specified protocols (http, https, tel, sms, mailto, ...) will be open using the corresponding system application. Of course, you can be much more specific by replacing the *
wildcards by actual values.
See this article for additional details.