The Ekiga softphone also khown as GnomeMeeting. Developer's site.
1. Download free version of Ekiga softphone from developer's web-site and start installation.
2. Start application, then click Edit tab in top menu, then select Accounts.
Also you can open Accounts window by combination Ctrl + E.
3. Click Accounts tab in this window and select Add a SIP Account in menu.
4. Enter profile name, for example, MCN.
Registar: enter SIP-domain address from registration email
User: your SIP ID
Authentication name: your SIP ID
Password: your SIP password
Enable account: on
5. Click OK button. Close Accounts window.
6. Your account is configured. To start a call click to the dial pad button as shown on screenshot below.
Your application is ready to use!