Today I came across an interesting offering: cheapvoip.com
This is a provider of voip telephony. This makes it possible to call fixed landlines in belgium for free from a computer (free software client, comparable to skype) or supported sip enabled device.
In practice this means anyone can call me for free (you have to create a free account, and buy credit for at least 10€) on my company phonenumber, which is routed automatically and for free (costs paid by my employer) to my cellphone.
Another interesting offering is phone2phone voip calls, where you let cheapvoip set up a call between two parties at interesting rates. Usually this is cheaper than calling yourself, especially for cross network calls.