The three major providers (Telekom, Vodafone, O2) now have real unlimited plans. It's around 80€, which is expensive, but not excessively so. We generally have far more expensive plans in Germany than anywhere else in Europe, which really sucks. The unlimited plans were first introduced at the end of last year if I recall correctly.
At least Telekom doesn't. I have an unlimited plan and use the three SIM cards for my home internet, my phone, and my iPad. Combined, I have hundreds of GB per month of traffic I use. I have the Magenta Business XL plan (not actually a business plan). It's LTE Max, so I get about 250MBps down, 50 up in Berlin. The same unlimited LTE traffic is now available as an 80EUR plan. Although to get to the same feature level (multi-sim, free international calls), I'd end up paying >100 again anyway.
Just looked at my home internet stats, that connection alone had 115.42 GB of download traffic over the past 5 days.
For comparison, I have an unlimited plan from Telia (Finland) with network speeds up to 200Mbit/s on 4G, no data caps and 15GB of roaming "EU-data" for 23.90€/mo.
Man, I'd kill for that kind of plan. I spent a year in Austria ages ago, and even they have substantially cheaper plans that still had higher data caps than German ones.