The Wi-Fi is fine. It is the cellular.
I tried reseating the SIM yesterday and it made no difference. Then tried the SIM in a different device. It worked fine. When I put it back in the original device, it connected again to Telus...so it is fine again for now. It just happens randomly and I'm not sure how to resolve it...whether it is the SIM or the device.
If it is not happening simultaneously to both devices, it is not likely the carrier. SIM cards rarely fail, but you can purchase a replacement very inexpensively from a Telus dealer. The most likely culprit is the phone, as it is the more complex device.