Do I have to give up my German number if I take a Bulgarian SIM card?

No. Almost every smartphone of recent years runs two numbers at once, either through two SIM slots or through an eSIM that the shop adds by QR code. Your German number stays reachable, and that matters more than it sounds: your banking approvals, the tax office and official post all hang on it. The Bulgarian number takes over daily life on the ground, so parking, tradespeople, deliveries, doctor's appointments. Before you travel, check in your handset's menu whether it supports an eSIM; older models need the second slot. How to get the card is covered in the section on phone number and internet.