The 855 area code is a toll-free area code for use in the United States and Canada. It’s just like the 800 area code in this respect. It isn’t tied to a geographical region within North America, and it is used by a lot of legitimate businesses. It is also used for illegitimate purposes, so its safety is debatable.
This message is created by your caller ID and not the phone carrier per see. It means that the number used to call you is outside of recognized regions according to your caller ID. In reality, it mostly means that the number doesn’t match any records on the caller ID database, so it could be coming from anywhere.
In North America, 324 is a reserved area code, which means that it is not currently in use in any region. While no country used 324 as a country code, Belgium uses 32, and Ghana uses a prefix of 233. Both of these can end up looking like they are a 324 area code when a caller ID has formatting limitations.