If you intend to use the Check-In/Check-Out with a new smartphone, make sure that this smartphone meets the technical requirements.
Your account is linked to your phone number. If your number remains similar, you will be able to log-in on your existing account.
New mobile phone number
If you change your mobile phone number you will be required to register again (= create a new account), as the user profile is linked to the mobile number. You will, therefore, lose your travel history.
Change of mobile network provider
If you change your mobile network provider without changing your mobile phone number it will continue to work.