Calling over wifi- What are the minimum broadband download and upload speeds needed?

I am possibly moving to a new house with bad mobile coverage. The broadband is not very fast as well. I checked today and the download speed is 2.09mbps and the upload is 0.24mbps. Does anyone know if this would be sufficient for me to use the a wifi signal to make calls on my blackberry? I would be situated near to the wifi box so it won't have to travel distance to my phone

Any help with this would be much appreciated

Yes. voip (which is what this is) would have worked back in the 54k modem speed days. (that's 0.054mpbs) ;-)