Configuration for Zoiper for Cal.net. As of update vs 1.38, July 13 2016.
Config > Accounts > Add Account/Config account
Account name can be anything
Host: office.cal.net
Username:[provided by cal.net]
password:[provided by cal.net]
Outbound Proxy: 216.57.71.135:5060
Go to Network Settings >
Disable “Use RPORT for signalling”