Ask HN: What do you use as secure Skype replacement of phone–computer calls?

There are alternatives to Skype for secure computer-to-computer text chatting and secure computer-to-computer voice or video chatting, all encrypted, free and open source.

But what if you want to call Aunt Maggie's mobile phone in Christmas without using paid Skype-out? What if you want to receive calls from Aunt Maggie in your computer without resorting to a Skype-in number?

What do you use?

Not interested in phone-to-phone. Paid service is ok. Better if libre open source, simple to set up, privacy-oriented.