That's a cool retro conquest, actually - and those USR Couriers really are the Lexuses of 56k modems.

One curiosity though: Almost no ISPs support USR's x2 56k protocol. Most support Rockwell's K56flex (or whatever it's called) alternative. So I'm surprised you're connecting at speeds greater than 33.6k.

I know it was possible to flash the x2 modems to k56flex - perhaps these were flashed, or perhaps they're later Couriers with both 56k protocols in firmware?