Can anyone help me with this.

I currently have a blackberry with cingular, I do not use it as a phone, I have unlimited date transfer on it with the international option, so it is free for me to surf the internet and receive/send emails on it when I am overseas.

However is there a way that I can purchase a SIM card when I am in Paris next week which would allow me to use it as a phone even though I do not have a voice plan on it - would I have to call cingular to unlock it and would I need them to do anything else to it so I can use it as a phone?

Thanks
Kasop