1. Open "Telephony - Telephony settings" on the bottom left bottom of the page. Then select "Connect SIP PBX".
2. On the next page click "Connect IP PBX".
3. Enter the following data:
Name of connection: Zadarma
Server address: sip.zadarma.com
Login: Your sip number (for example 111111) from personal account
Password: Your Password of sip number from "SIP Connection" in personal account.
Then click "Connect".
4. If the information was entered correctly, on the next page the connection status will appear as "Connected".
Save settings and you can now use the telephony.

Note
When connecting to Zadarma IP PBX you need to use the internal IP PBX information that appears under "My PBX - Extension numbers".
Server address: pbx.zadarma.com
Login: Your internal PBX number (for example 1234-100) from personal account
Password: Your Password of internal PBX number from personal account
After that click "Save".

Operation aspect:
1. For further usage of outgoing calls in Bitrix24 You have to pay connection of "SIP connector"
2. Numbers are dialed in international format with + . For example: +44 204 577 00 77