It's worth noting that the billing methods for US and the rest of Europe are very different when it comes to voice. For instance, it costs between 4c/min to 26c/min to call a UK mobile phone. In the US it's < 1c/min. Outside the US, the caller of a mobile phone is generally the party footing the bill for the entire call.

The more interesting question I have is why would it cost 26c/min to call a mobile phone? And since each carrier prefix may have a different cost, how do consumers keep all these prefixes / carrier rates straight in their heads?

Edit: I'm looking at flowroute, plivo, and twilio.