For years you can have a couple of lines on the same SIM/contract (common in Europe for people who run small businesses etc) maybe its just for flicking between the two lines?
eg. 078900056321 (line one)
078900056322 (line two)
Orange were always big on giving second lines on accounts, and they recently became official provider in the UK
edit - just read where it was, so not a toggling option. not sure how the line gets swapped on other devices but I use to deal with a small company where the owner had it set up on his Orange contracts on Nokia handset.