Hello Ryan505, thank you for reaching out to us on the Forum. I am sorry to hear your having issues with your device. I would like to provide you information regarding your device situation.
With Xfinity Mobile, we offer the option to bring your own device (BYOD) however, this is limited to Apple, Samsung, and Pixel devices. We are working to expand this option to all devices, old and new, however, we do not have an estimated time for when this will happen or be available. Your Razor is not listed as a compatible device with our network, you can swap your sim into that device at any time. Keep in mind, since it is an unsupported device the connection and functionality are not guaranteed.
I know this is not the best answer, we can still help you get your iPhone and or Samsung reactivated on your line. We also have a selection of Motorola devices available for purchase. You can check out our website xfinitymobile.com, for the full device line up. You can also keep checking your device compatibility through our BYOD program. Here is a link to do so;
I hope this provides clarification for why your device is not working properly. Please let me know if you have any further questions, as I am here to help.
@Ryan505 Were you ever able to get this resolved? I am also trying to get SMS working on a flip phone (current LTE model from Verizon/unlocked). I've read about 'premium message blocking' being the issue, but am not sure if I would get the run around from Comcast support, too.