Bandwidth SIP Account setup

First, click the main menu button in the top-left corner of main window.

Then click Settings in the main menu and navigate SIP Accounts section at the left panel:

Click Add Account button:

Now enter your SIP account credentials you got from Bandwidth in the appropriate fields:

Account name — name it somehow
Register on startup — the program will do SIP registration for this account if it is ticked. If no, the program doesn't register on a SIP server, so you might not be able to place or receive calls.
SIP server — SIP server hostname or IP address. Program uses 5060 port to connect a SIP server by default. You can define other port using that format: sipserver:5061.
Login — the login
Password — the password
Display name — this is what callee will see
Authorization name — the program will use Login for authorization if this field is empty
Domain — SIP domain
SIP proxy — SIP proxy

Click Test Connection button. You'll see the Successful registration message if Softphone.Pro can register on a SIP server.

Click Save button to save your SIP account settings. Everything is OK, you are brilliant :)