Vodafone Germany offers call ya sim (prepaid sim). I have used this and this provides voice as well as data. Data using APN event.vodafone.de costs Euro 3.95/ day for 1GB and Euro 12.95/ 7 days for 1 GB. Data speeds are good ranging from 1.5 Mbps to 3 Mbps. Latency is low at 79 ms and so response on Internet is quite fast.
You can also cut the sim using a micro sim cutter and use on an iPhone which is unlocked. But use APN as event.vodafone.de for getting data.
Good for travelers to Germany.