I was at a friend's house who uses VOIP on his own private WiFi for his phone calls. He made a call over VOIP (Voice Over Internet Protocol) that included the need to verbally state his credit card number over the telephone (he was ordering food).
After the call, he turned to me, and asked: "Is it safe to give out a credit card number over VOIP?". I told him I didn't know, but would ask here.
So the details are that he uses mainstream VOIP providers and his own WiFi (secured as best as WiFi can be secured). For this Q/A, let's assume that no one has hacked into his WiFi and that there were no problems at the restaurant from where he was ordering food.
Now, obviously, there is the risk that the person at the restaurant can easily steal his credit card information, but that's an assumed and understood risk.
The question here is: Is VOIP reasonably secure for this kind of use? Another way to put it: Does VOIP have about the same level of security as a landline, or does it have more, or less?