Check out this option in Your Smartphone.

Check out this option in your internet connected devices.
smartphone
If you are using a Smartphone and when you click on a phone number in a web site, what does your phone do next? Ask your permission to proceed with the call or simply continue with the dialing.

If it asks whether to continue with the call is good procedure.
Other wise there are chances for your Smartphone to dial premium phone numbers automatically and to bring you huge phone bills at the end of the month.

Specially many Apps have the facility to dial those numbers that can give you huge phone bill. So check out your device OS perfectly to see if the function can be done with out notification or through the installed Apps to use the dialing facility with out your permission in the future.