[michaelw]

You can do some pretty cool stuff when you're an MVNO. No need for custom dialers (which wouldn't be much fun on iOS anyways).

The system uses inbound calls, calling history and contacts to learn how to handle outbound call. User preferences control the defaults.

Get a call from Fred on the first number, all calls to Fred will use that number. Make a call to Mary with the second number, future calls to Mary will use the second number.

Throw in multiple sets of contacts from your work and personal email accounts and it's going to be pretty smooth.

Full disclosure: the co-founder is a friend. I have no involvement in Mast though.