Finally got around to using the last feature on my VOIP setup (I'm already rejoicing in the fact that there's no line rental, making it rather cheaper than having a fixed line, as I make about £3 of calls a month). I called the US. For 1.5p/min (that's about 2.5c). Nothing special - but Cafepress was rejecting my credit card, so 5 minutes on the phone to a helpful guy on their helpdesk and I had it all sorted out.
For some reason being able to make phone calls to the other side of the planet without worrying about the cost seems more impressive than sending emails there :->
