It looks like calls are FREE until the end of the month.
I emailed them to see what the costs would be for us guys in the USA to make calls but they did not have pricing.
I'm trying to decide if I want to try Truphone out, but not just for a few weeks. So I'm waiting until USA pricing comes out.
And I just checked again.
There is still no updated pricing for calls in the USA, it still says FREE.
I'm sure it wouldn't be more than a few cents a minute.