Thus,
I decided to go for a test to use voip over 3G on Vodafone Ro carrier by paying the low fee of 3.13 Euros. Firstly, I must say that it works like a charm. If you make a calculus - after I finish my included minutes in the plan carrier the cost of this is quite afordable, taking into account the international calls I go for.

G, N900 User.