I have used the T-Mobile free data service in Europe and it's not too bad as far as speed goes. It generally is a 3G connection that's throttled to 2G, so it's great for navigation, using Yelp to find restaurants, email, FaceTime and just about any text based website like this forum. For that I pay $10 a month (I have a 3rd line on a Family Plan), and get $.20 a minute phone calls, FREE TEXTING, and free FaceTime Voice. I realize DT is a large provider in Europe, but we're talking a HUGE difference in rates here.
All that aside, how do you justify the Verizon 100 Mb cruise data of $25 vs. $120 for the same 100 Mb on AT&T? To use your Deutch Telecom comparison, shouldn't AT&T be substantially cheaper because of it's partnership with MTN? So, how can VZ afford to give away the farm charging so little?
I currently use KeepGo for high speed data in Europe also. It's $6 a day for 100 Mb per day, roams on AT&T partners, and works great. They resell AT&T data for a lot less than AT&T sells the same access. Eight days worth of service with 800 Mb costs $48, vs. $120 from AT&T for the same amount of data. If I want only 50 Mb per day, the daily rate drops to $4.
I think AT&T sees cruise ship service as a cash cow and is in no hurry to adjust rates to be more in line with costs. Like I said, if VZ can offer substantially lower priced access, AT&T should be able to beat or at least match their prices easily.