For which area you want to use your phone?
Without knowing your location i can't tell the correct network for you.
So Go to a phone shop in town, tell them what you want, they can advise.Before getting your cell phone service provider,Make sure your phone is unlocked and accept that carrier,If it's restricted by other network carrier means,You will need to unlock your phone.For unlocking you can approach your current network provider or else try to buy an unlocking service from any one of the online unlocking service provider like UnBBLock.com They will provide an unlocking service for Blackberry mobile models only.If you have other than Blackberry phone use Unlock-Zone.com I hope it will be very useful to you.