Rayservers offers SIP service where you can use ZRTP plus VPN protection. When you purchase service from us, you will get details that include:

Extension/username: assigned
Password: assigned
SIP Registrar: openser.rayservers.com

You will also get a long distance PIN to make (insecure) calls to regular telephones.

ZRTP secure audio with softphones on Linux, Windows and Mac

ZRTP on Linux

Linux comes with Twinklephone, a full open source ZRTP client. We recommend Ubuntu or Debian Linux on the desktop with Twinkle 1.4.2+. You can create 100% encrypted laptops with a open source operating system which is your best guarantee against back doors and add the AES 256 VPN layer as well. This is the most robust security for communication available today, and you can prove it to yourself that no one else but you and your partner can hear what you say.

To install Twinkle on Ubuntu or Debian Linux:

From the desktop: Go System -> Administration -> Synaptic Package Manager. Search for and install twinkle.

From the terminal:

sudo apt-get install twinkle

When prompted for your settings, enter your SIP account details

Tweak your twinkle

The important settings which you may have to change are listed below. If its not listed, do not touch it.

Visit Edit -> User Profile

User -> User name: <your extension assigned by Rayservers> example 8888
User -> Domain: openser.rayservers.com
User -> Authentication:  <your extension assigned by Rayservers> example: 8888
User -> Password: <your password assigned by Rayservers> example: VB4DUT8

SIP Server -> Registrar: openser.rayservers.com
SIP Server -> Expiry: 60

RTP Audio => Active Codecs [from top to bottom]

Speex-wb (16 KHz)
Speex-nb (8 KHz)
GSM
G711u
G711a

Follow codec preference from far end on incoming calls: unchecked

Follow codec preference from far end on outgoing calls: unchecked

Note - if you have poor bandwidth, promote Speex-nb (8 KHz) to the top

Security => 

Enable ZRTP encryption: checked

Only Encrypt Audio if remote party indicated support in SDP: unchecked
Indicate ZRTP support in SDP: checked
Popup warning if remote party disables encryption: checked

Twinkle on Linux will make calls to and from the Zfone plus softphone setup described for Mac and Windows using Speex-nb (8 KHz)

If you have a USB headset, you will have to choose it in Edit -> System settings -> Audio devices

ZRTP on Mac and Windows

Download and install Jitsi - a multiplatform SIP+ZRTP client that works on Windows, Mac and Linux.

Start making secure calls.

You can also install the AES 256 VPN layer as well to protect all your network usage.

You can call support securely on 1001. Echo test is 600.