Hi,

A mate of the girlfriend's is off to Thailand next Thursday (no, I'm not sure why either )

She has an old BB Curve 8900 that's locked to Orange that she'd like to unlock to take with her and get a local SIM to put in it (I think that'd be cheaper than taking an Orange SIM and using it over there, right?)

So, How can I unlock the phone? Do I have to get an unlock code from Orange? Is that free? Or, can I do it via another method?

Cheers,
Craig.

If you call orange then they should provide you with the code and instructions for doing it. Or is you search online there are many websites that will generate a code for about £3.99. All you need to know is the IMEI number of the BlackBerry as the code is generated uniquely using this.
The unlocking process is quite simple, again you can find instructions online.