Will my phone number automatically change if buy a new sim?

Yes, if you buy a new SIM card, your phone number will change. Each SIM card is associated with a specific phone number, so when you activate a new SIM card, you will be assigned a new phone number.

No, your phone number is usually associated with your account with the mobile service provider, not with the physical SIM card.

When you buy a new SIM card, you can activate it on your account and transfer your existing phone number to the new SIM. This process is typically handled by your service provider, and you may need to provide some account information or follow specific instructions.