Yes, you can make a call to any number if you have enough credit balance.
However, there are a few exceptions to the above given these are the exceptions imposed on our underlying technology - VoIP.
- Special short service numbers that are operator or circle specific may not work
- No support for USSD service
- A few countries, where Internet-based phone calls are restricted, controlled or prohibited
With that said, practically, you can use this app to real phone numbers pretty much similar to how you are using conventional telephony services.