You should be aware that once a Blackberry is registered for Blackberry Internet Service with a certain operator you can not activate BIS with another operator. So if you have activated BIS with T-Mobile USA your device is tied to them and you won't be able to get BIS for your device with any other operator in the world even when swapping SIM cards.
We discussed this issue in detail
here.
You can use another SIM card in your Blackberry and use it for calling, but you cannot get BIS on it with another SIM card unless you cancel BIS with T-Mobile USA.