You will need a SIM that's registered with the provider with an Blackberry Service Add-on to be able to use BBM (BlackBerry Messenger) and BlackBerry emails. You will then need to inform the service provider your BlackBerry account (if you have one) and your device PIN which is locate in your handset under Setup > option > device > Device and status information.
If you don't have a blackberry account, you can register for one after you have put the SIM in the BlackBerry and the service provider have register your device on their blackberry network (usually automatically after you switch on the device). To register a blackberry account you can go to the provider's BlackBerry portal. i.e. optus.blackberry.com.au or telstra.blackberry.com.au and etc. You will need the device PIN and the IMEI number and your email login detail to register.
Once you have successfully register your BlackBerry account, your email should start coming in in about 3 minutes.
If you already have a BlackBerry account, simply login to you account through the provider's portal to update your new service number.
Hope this helps!!