Wether the VOIP Calls Are Secure or Not?

VoIP travels primarily over the Internet, except when originating and terminating through local phone companies lines. By default, most VoIP connections over Internet are not encrypted. Anything over Internet cannot be considered secure if it is not encrypted. Just like email is not secure over Internet unless it goes through a secure encrypted connection, or the email itself is encrypted.

VoIP can be encrypted, but most connections are not handled as such. Skype is one of the few VoIP services that has Always encrypted all communications over their system.

Keeping in mind that even if VoIP calls were encrypted by the VoIP carrier, it would only be encrypted over their network or while on the Internet. As soon as a VoIP call bridges onto the PSTN telephone network (like through your telco), it is no longer encrypted anymore.