Sorry...they answer to your questions are ...very little...Yes they can...if it is a Nextel they can put the handset on a list but that will not stop somebody from putting an activated SIM, at least a Boost Sim, into it and taking off like it was always there's....
You should definately report it as stolen to your carrier. But don't expect much action on getting it returned.
The IMEI (msn) will show up in an open and active account when somebody try's to activate it, but there are ways around that issue, the activating agent should act responsibly and tell the customer to contact Nextel to get them to release it before he/she can activate the equipment, but....

Sorry Blast....Jess