Voipbuster – update
I just recieved news that Voipbuster now offers free dial-in-numbers in Austria. I know this sounds like a paid ad, but I really like this idea:
Neu! Gratis VoipIn Nummer für alle Österreichische Voipbuster Nutzer!
Besuchen Sie http://www.voipbuster.com/en/buycredits.html. Fragen Sie eine GRATIS Österreichische VoipIn Nummer an. Achten Sie darauf, dass sie dafür über ein Guthaben verfügen müssen.
Mit einer VoipIn Nummer kann jeder – auch Leute die Voipbuster nicht nutzen – Sie auf dem Voipbuster erreichen.Bei Skype zahlen Sie 30 Euro pro Jahr für eine VoipIn Nummer, bei Voipbuster bekommen Sie die Nummer GRATIS!
All you need is a one time 10 Euro deposit, that you can use to call later on, and you get free calls (landlines only, no mobiles, but for that you can use your 10 Euros) to Argentina, Austria, Denmark, Finland, Germany, Greece, Ireland, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, Taiwan and the United States as well as a call in number for those who have no computer available and want to call you nonetheless.
I must admit, if I had to pay 10 Euros, I would also think about it twice, but when I subscribed, it was only 1 Euro 
—— UPDATE ——
I just found another Page, which uses the same system (at least the same client, although with a more agressive color scheme, as well as the same database): VoipStunt. They seem to be based in Germany, not in Swizerland like the VoipBuster, and they offer free calls to more contries.