You need an unlocker to do this. There are stores out there that can do this for you for a small fee. Its a machine you hook your phone up to and it basically takes thkes the lock code off if you use a sim card from another carrier. If you know someone that works in the tech dept. for a carrier, sometimes they have the unlock codes for certain units... It easier if you have the machine.
How long have you been with that cellphone carrier? I assume you get your V600 from them. Most of them will unlock your phone if you are with them more than couple months. Just tell them you are going to travel overseas and use one of those prepaid sims over there.