The article linked by thesimon states "UPU member postal services are obliged to exchange an IRC for postage, but are not obliged to sell them" so it looks like this would work. They cost 2€ here in Germany ($2.20) compared to $1.20 for a USPS First-Class Mail International Letter, so it's not that bad. Really cool!
And this would nicely keep with the whole theme, since Ponzi's original scheme involved arbitrage with IRCs, before he decided it would be easier to just rip people off.
