The import is rejected by customs. Yes, this means there's the small loophole of traveling to another country (which is usually a long travel, this country is huge and the ocean is wide), buying the phone there, and bringing it back with you.
I don't know whether the carriers do reject phones with IMEI pointing to a non-homologated model used with a SIM registered to a Brazilian carrier (that is, not roaming).
> If it's IMEI-based, then probably you can still have an alternative phone that will use WiFi hotspot from the "certified" one.
That takes me back, it's exactly how I used my pre-smartphone PDA, tethering to my phone through Bluetooth. Yeah, that would work (it's exactly how I use my laptop when I can't use the normal Internet connection), were I able to import the thing in the first place.