Your €29 monthly plan includes 22 GB of data per month. Converted, that is 0.7 GB of data per day. So during the seven-day transition period before your first bill, you can use approximately 4.9 GB (0.7 GB x 7 days). The price of your monthly plan for those seven days is also prorated (€29 / 31 days = €0.93 per day for 7 days).