There are carriers that do much better than this, right? T-Mobile (my carrier) allows unlocking postpaid plans after much less than 2 years, and I had no trouble at all calling them and saying "Hey, I'll be in Europe, unlock code plz" despite not having paid off the device.

https://support.t-mobile.com/docs/DOC-1588

Surely someone's made a nice table of carriers and policies?