Vodafone Germany have been declaring their 3G sticks as SIM- or netlocked since they were introduced. But in fact the only restriction their sticks have had so far is the dashboard software, which doesn't connect to non-Vodafone networks. But if you download an unbranded dashboard from the web (like ZTE Join Air), you have a completely unlocked device. And by the "hard method" mentioned above, you can even replace the installation files in the flash memory of the stick, so your stick will automatically install ZTE Join Air instead of Vodafone's dashboard if plugged into a new computer.
If you still have doubts, check the user comments on this recent Vodafone promotion at
mydealz.de. There you'll also find instructions on how you can get that 3G-stick practically for free by registering for a cashback-serivce called qipu.de. These guys will refund € 10 by bank transfer or PayPal shortly after ordering the stick through a referal-link on their website. Regardless of this refund you will have to pay € 10 for the stick in cash on delivery to the delivering parcel service.
Of course this refund is only available when ordering online.