All SIMlocked phones purchased in Germany can be unlocked free of charge after a period of 24 months. However therefore you'll need to send a proof of purchase to the operator, the phone is tied to, which is Vodafone in your case.
Vodafone also has a
form for retrieving unlock codes on their website. Maybe they record when phones register on their network for the first time and so they can determine the age of the phone even without proof of purchase.
Just find out the IMEI (serial number) of your phone by entering *#06# or looking below it's battery and enter it on the linked page. If you're lucky you'll get your unlock code within seconds.
In any case let us know if you succeeded.