1. Download X-Lite here
2. Open "Softphone - Account settings"

3. Enter the following:
Account name: Zadarma
User ID: Your sip number (for example 111111) from your personal account
Domain: sip.zadarma.com
Password: Your sip number password from your personal account
Display name: Your sip number (for example 111111) from your personal account
Authorization name: Your sip number (for example 111111) from your personal account

Account name: Zadarma
User ID: Your PBX extension number (for example 1234-100) from your personal account
Domain: pbx.zadarma.com
Password: Your PBX extension number password from your personal account
Display name: Your PBX extension number (for example 1234-100) from your personal account
Authorization name: Your PBX extension number (for example 1234-100) from your personal account

4. Softphone status is "Available" and you can make calls.
