I suspect that Huawei devices are locked to a particular network. So if, say, you bought this device
https://www.pcworld.co.uk/gbuk/phones-broadband-and-sat-nav/broadband/mobile-broadband/three-pay-as-you-go-3g-mifi-10023991-pdt.html
you'd need to use a Three SIM. So, to try what you're suggesting, you'd obviously need to use either an unlocked phone or a phone locked to Three for the registration process.
However, depending upon how the provider's system works, you might then end up with a 'data+calls+texts' account (for the phone), rather than the 'data only' type that you'd actually need (for the wifi device).