We appreciate you bringing this concern to our attention. I am more than happy to help. Switching the SIM cards between the phones will not void your qualification for the $250 gift card. Receiving your $250 gift card depends on keeping your account in good standing for 90 days.
Switching the SIM cards between the devices creates an unsolicited device status on your account. Such a status will prevent you from making changes to your account, for example changing your data plan.
Did you want to make a permanent change to your account and switch the devices from one mobile number to another? Let me know what your intentions are. You can reach out to me through private message by clicking on my name ComcastChrisL and then click on send message.
Make sure to include first and last name of the account holder, the account number, and the last 4 digits of the stored payment method on file. After I authenticate the account, I will investigate this for you further.