How to unlock a Blackberry
I think the first thing I'd like to say is that, contrary to popular belief, it's completely legal to unlock your mobile phone. The reason phones are locked in the first place is so you'll remain "faithful" to your current network provider.
Now, onto the good news. Yes, you can unlock your Blackberry, and I'm going to tell you how below.
There are two options available to you when considering how to unlock your phone. One of them requires a fairly complex technical route, so I'll ignore that one, and focus on the easier option - using a code.
How to use a code to unlock a Blackberry
The type of code you'll need to unlock your Blackberry depends on the model. Your best bet is to try GiffGaff.com - simply locate your model and follow the instructions they provide.
A few words of warning about attempting to unlock a Blackberry
Although it's perfectly legal to unlock your phone, some codes don't work and it may take a little time to find the right one. You should make sure that you don't exceed the number of code entry attempts. Doing this can completely lock your phone.
The guides provided at GiffGaff are free to everyone, so don't expect the code to work instantly. There are other sites out there that offer paid unlocks, and although it will set you back a few quid at first, you're likely to receive a guarantee that the unlock will be successful. Network providers usually allow you to purchase an unlock for a reasonable price, to check with your provider first!