Install app linphone from Google Play.

Select "Let's go" -> "I already have a SIP account", fill in the data as follows:

Enter the Username and Password you received when registering (username of the view 3XXX or 1XXXX) and domain:

Click "Apply" and go to Settings -> Network

STUN server: erase, leave the field blank. Transport: TCP, UDP is available. Set UDP.

Congratulations! Now you can call!