Hi follow the procedure to know whether your Blackberry 8100 mobile is locked to network or not .
Switch on your mobile phone with a sim card from a network other than the network you are currently with. If you are able to use the phone, you can be sure that your phone is not locked. If your phone displays an error message saying
"Wrong sim" or
"Incorrect sim" or
"Emergency calls only", etc., then your phone is probably locked.
If it is locked then unless you unlock it you cant use it on other network .To unlock it visit
Classicunlocking.com here they ask you the network name to which your mobile is locked and the IMEI number of your mobile .Then they deliver you code to unlock your mobile.