Hi,
BIS is the Blackberry Internet Service.
It is required for the blackberry to connect to the internet, BBM, and email services, as they travel a slightly different way around the mobile phone networks to normal data.
If you get the handset and contract at the same time, then there is a high chance of the contract being designed for a blackberry and it being included.
Always best to check if you can though, as if it's a standard plan, there shouldn't be an issue changing it to one that supports blackberry, and there shouldn't be any difference in price.
