Here I offer to you dayflats for internet use with a German O2 prepaid sim cards. Just topup the sim for the dayflat the same way as a topup of money. The dayflat is always valid from the text-message confirmation until midnight and contains a full speed access for one gigabite. After using this gigabite the traffic will be reduced to GPRS.
Please remark: This dayflat does only work in combination with an O2 sim-card like O2 go or O2o, not with the actually tariffs like O2 LOOP smartphone or O2 loop.