Reviews on any major VoIP operator are different, not all decide to configure SIP hardware/software.
More interesting conditions than the Balance on the room You will hardly find in the market:
zadarma.com/ru/number800/
Besides rooms there are ATS, but free, and a lot of Goodies.
And most importantly, no one bothers to sign up for free, and to test calls (both outgoing and incoming, through a number of extend).