Carriers lock the cell phones and to use them on a different carrier you need to get the unlock codes either from the carrier or by purchasing the codes. If you decide to go that route then you need to follow all the requirements when entering the numbers.
This is not specific to Blackberry phones, all have locks.
Vodafone offers a method to do this on their web site. https://unlock.vodafone.com.au/voila...=selectService