Navigate to https://desktop.jitsi.org and select "Download Jitsi", then "stable builds", then choose your operating system which is likely either "Microsoft Windows Installers" or "MAC OS X packages"
Click on the downloaded package to install on your desktop or laptop. Under the Additional Tasks setup window, uncheck the "Make Jitsi the default Instant Messaging Provider (Outlook integration)" and click "Next", then "Install".
To setup your Press8 softphone account:
- Obtain your username and password from Press8 support.
- Choose "SIP" as your account type.
- Enter your username in the form of <username given by support>@sip.press8.com, so an example would be something like "email@example.com".
- Enter your password, then "sign in".
Your softphone should now indicate "Online".
To receive notice of new messages, go to Tools > Options and double click on your SIP account. Under the connection tab, select "Message Waiting (MWI)" check box, and enter <your extension number>@sip.press8.com. So in the example above, that value would be firstname.lastname@example.org. Click "Next", then "sign in".
The only way to check messages is to dial "*1".
More detailed installation instructions may be found here: https://desktop.jitsi.org/Documentation/InstallAndSetupOnWindows
User documentation is very limited for this free product, however, Jitsi is capable to complete blind transfers using the transfer button revealed when you have an active call. Simply click on the transfer button, and enter the transfer to destination (which can be a full 10 digit telephone number or a 3 or 4 digit local system extension number). You will not have the opportunity to talk to the party receiving the transfer.