Originally Posted by geekmaster
They flip the switch in your account, tied to your serial number. For the existing eink kindles (when ordered as a "gift" so they are not registered), they ship as non-SO, and start displaying ads shortly after you register them.
You can also test that with a FULL "factory reset" (back to new-in-box condition), by erasing the persistent user store (not USB drive) partition, where all your settings are stored.
The shipping of non-SO models first is (probably) just a non-technical policy decision. Perhaps to start generating SO ad revenue early in the shipping schedule?
In that case there must be another reason why the SOs ship first. Maybe Amazon has some kind of agreement with the advertisers.