Despite Berlin's general lack of parity with modern technology, I've never actually had a problem with internet access across the ubahn network in the past decade. I noticed that certain carriers used to have very different availability when travelling and so switched to a better one, but I was always surprised at being able to handle mobile data whilst underground.
Wow! I was in Berlin last week and kept losing connection... like all the time. I use 3 with a Swedish plan. In Sweden, it literally never drops, not on trains, not on metro, not on faraway mountains... it works everywhere.
used to have spotty coverage underground with vodafone, when i switched to telekom, internet suddenly magically worked underground on the routes i used.
I believe someone published a map of the data coverage of different providers on the berlin ubahn, but probably outdated now
Yeah, admittedly this year I've also started experiencing holes on the ringbahn (strangely and consistently around frankfurter allee), but the ubahn has been fine.
I'm with sim.de which I believe is essentially an O2 reseller (apn references o2)
