Viewing the English page, the FAQ says that the free calls are limited to one minute.
http://startel.pt/eng/faq.html
See Items 1.6 and 1.7.
Not sure what they mean, because I thought I can only register my own number, not destination numbers, and obviously there is no VOIP path to a pure landline number (otherwise, I would call it directly).
Their rates are quite reasonable otherwise.
Tried to register yesterday, but did not receive a confirmation email yet.