Your BlackBerry ID username and password gives you access to BlackBerry websites, apps, services, and back up your blackberry messenger information like BBM contact and BBM group.
It helps sync your information with your computer , and transfer that information when you change devices. One BlackBerry ID can be used for all your BlackBerry devices.
So Blackberry user can transfer their BB contact from old Blackberry device to Blackberry with OS 10
like Z10,Q10 ...
source : http://us.blackberry.com/bbid.html
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