Phones are different. Only some phones (if any) self-brick on finding out from the cell towers they're black-listed. (If they ever do. For all I know they just see a communication error with the cell tower on their end. That's something I'd need to look up in more detail before commiting to an opinion.)

But the point is, you have to actually think about the phones you're talking about. Some dumbphone is very likely to appear bricked when blacklisted - some might just fail to boot if they aren't able to connect to the network. But I don't think it would make sense to assume all phones self-brick just because they get a "you're blacklisted" event from a cell tower.

The ONLY posts I remember from a user who seemed to have their N900's IMEI blocked (a user named Zimon - you can look up more indepth info if you'd like, or search for others) said he could boot fine, just couldn't connect to the networks of some of the providers in his area, but could connect to some other networks.

Also, if the starter of this thread lives in the USA, carriers never IMEI blacklist, based on what I've heard. (Verizon does, but that's for CDMA network equivalents of the IMEI, which isn't relevant since the N900 doesn't connect to CDMA anyway.)