I went to an O2 shop to buy a prepaid card from the S-bahn friedrichstrasse station yesterday, stating clearly that i only want the card for the data plan so i can use my iphone4 to get online. The guy there said that i can do that with a plan of 10Euros per month and that it should be activated in ten minutes.
After i paid and he gave me the card, he instructed me to call a number to top up the card and said that i should receive a sms afterwards. As everything he handed me was in german, i asked if he could help me do it, and he refused, saying that it is really easy, i only have to type in the number and call. So i did, and we waited for five minutes and there was no sms whatsoever, so he said it could arrive within 30minutes, so we went off to do other things.
However, after two hours, i still couldn't get online, so i went back to the shop and asked him for help. The apn settings didn't setup automatically as he said it would, and he said it is because the system is down and it might be for another 24 hours. I said i am only staying for a few days, so that means i am paying 25euros for a card that i cannot use at all. He just gave me an expression that he can't do anything about it, without any apologies, and meanwhile, his colleague next to him (who seemed of a higher position) was very impolite all along giving us an impression that he found us very annoying as we couldn't speak german.
In conclusion, DO NOT go to buy sim cards from o2 as they are really unprofessional and unhelpful and also impolite. Not mentionning that the cards dont' work at all and they staff dont' even want to help you solve your problem.