Switch mobile service providers is much faster and easier than it used to be, and you are always asked whether you'd like to take your number with you.
This process is called 'porting' and it is super simple. When signing up with a new provider you check the box which asks whether you'd like to port your existing phone number to your new service. You will need to provide the phone number and the account number you have with your current provider.
Once your new account is activated, your new telco will contact your old provider and initiate the port. Typically the process takes less than 2 hours and your old service will continue working until the port has been completed.
By law, you own your phone number and a telco is not allowed to block your attempt to port your number to a competitor.