I don't think there is an O.S map app for Blackberry phones, I've only seen Viewranger on the Playbook. Appworld,I know for a fact that Quo only supports windows phones and I'm sure memory map and anquet don't have anything for BB.
O.S maps by the way are Ordnance Survey Maps, used for hiking, mountain biking, green laning etc, highly detailed at 1:25000 or 1:50000 scale.
It would be nice if anquet or Memory Map had a bb app though ...... Please!