[CrackBerry Question]

I have an issue with a phone my company bought directly to the carrier (it's a professional use phone). I stopped for years using it since a got a new one.

Now I'm trying to use it as a backup phone but even without any SIM inside I get the message:
"Phone not allowed / MM#5".

My guess, after looking for an answer over the web, is that the phone was registrered (by mistake of the carrier) as a blacklisted one. Is that the meaning of the error code?

How can I handle that?