Can an iPhone be used abroad if imei is blocked?

if my phone (any phone) is stolen and I repport the IMEI to the police they have all the carriers block it

if those carriers have an agreement with carriers in other countries to block stolen phone IMEI's too then I guess it could be in more then one country but the local police would not be likely to take contact with carriers in other nations

You mean blacklisted? If so, blacklisting is generally limited to the country where the phone is blacklisted, as there is no universal world-wide blacklist.