No, you can use any smartphone as long as you download the SleepScore Max app and log in to your account. After logging in using the email and password associated with your account, use the app to pair the smartphone to your SleepScore Max unit.
When in range, your SleepScore Max unit should automatically re-connect with the last device it was connected to. Therefore, if you change smart device, ensure Bluetooth® is turned off on the device you do not wish to use.