Apple cannot backlist an IMEI, only the network can. If one has phone insurance with a third party, then the handsets IMEI must be blacklisted, otherwise they won't entertain any claim for loss or theft. It's also worth mentioning that should a network refuse to blacklist handsets that have been stolen, it puts its customers at a higher risk of becoming victims of crime by any criminal gangs looking to steal handsets, as they will know such devices' IMEI numbers will never be barred.
