I'm in Europe and bandwidth costs are relatively insignificant (as long as you don't travel abroad). Data roaming is whole different story, I really hope European Union will do something about it.
After two minutes, I sent out 652 KB of data and received 798 KB.
So this means that a minute of data is around 750KB.
My mobile subscription (Swisscom) comes with 250MB of inclusive data for CHF 35/month (around $35 or EUR 25).
With 750KB per minute, I can in theory talk for around 5.5 hours if I do nothing but Skype. My current data usage is around 50 MB/month, which leaves 200 MB unused which then is good for 4 hours of talk time.
Not bad.
I would have thought that a Skype conversation uses way more bandwidth than it apparently does.