iNomado

Once you have created an account on www.nomado.eu/eshop/signup.php

When you have filled your sip username and pass on iNomado (see post http://www.inomado.com/lang/en/how-to-configure-inomado-wih-my-sip-account/ ) you can start making calls.

You need to see that the SIP button is green like on the screenshot here:

How to be called on my nomado number?

On this version you can only be called if the application is open. Next version (very soon) will include Push notification and balance as well.