Are you sure you even need to unlock your phone? I assume you have a 7100 since you're posting in the 7100 forum. If so, this is a GSM/GPRS phone and will most likely function all over the world with the exception of a few countries.
You don't *need* to use a foreign carrier SIM in another country.
Your SIM will probably work just fine. You'll even keep your same phone number. If the foreign carrier has roaming agreements for data, then you'll even get to use your Blackberry data plan overseas.
Just ask your company to provision an International Dialing plan of some sort on your account, and you'll get discounted rates.
Unlocking allows you to use a foreign carrier's SIM card... that's about it. If this is what you need to do... then unlock it. Otherwise, why bother?