Your account will automatically be updated with the new number.
A device with Lookout installed can connect to our servers as long as it has a connection—either cellular or WiFi. So it doesn't even need a SIM chip in it to work with our service. If a new SIM is placed in the device, your account will be automatically updated with the new number when the phone next connects to Lookout's servers. We consider the phone number to be for reference only.
At this point Lookout doesn't alert you if a new number appears on your account, but if it connects to your account we will display it.
If your new phone number doesn't update correctly, please wait a few hours. If you are still having trouble, please contact us at firstname.lastname@example.org
Note to iOS users: We do not detect phone numbers on iOS devices, so we can't update your settings if a SIM was replaced.