[joelhaasnoot]

There are some countries you do have to give extra documentation, and often providers will rip you off by giving you more airtime only if you register.

Funny you mention Ethiopia, the telecom there is completely state controlled, and it has been used to thwart opposition (listen in on calls, shut down complete SMS, etc). It's one of the many "remnants" of the communist regime. Supposedly Orange was coming in to manage and change that however...