On Android only you could use the venerable SipDroid application, freely available via Google Play. However, please keep in mind that it has not been updated in a long time and there have been reports of security issues.
This older app is quite straightforward to configure.
More specifically,
Start the SIP Droid Softphone
Go to Sip Account Settings
Fill in your information as obtained from Control Panel - My Services:
Authorization User Name: YourUserID (Optionally, you may enter at Caller ID how you want your name to appear on outgoing calls.)
Password: YourPassword
Server: YourDomain (e.g., toronto1.ezvoip.co or replace "toronto" with your city)
Enjoy!