Generally the phone needs to be unlocked which you can have done. Once free to connect to another network provider allyou then need to do is contact a local carrier that supports the blackberry service. you will need a full blackberry Data plan to use BBM.
If you only going to be there for a few months, it may be easier and less cost to simply get a local month to month phone.
If you decide to unlock the phone this may help with the process you will need to follow. do a search for the specific BB you have for detailed directions. Unlocked Storm on AT&T or T-Mobile