On another thread someone was talking about small mobile operators going bust and people losing their number and credit.

What happens when someone like Sainsburys decided to close their mobile service? Obviously they didn't go bust it just closed. Did they transfer everyone on to straight O2?

Which other mobile services have closed? Easy Mobile?

Their landline service customers were given the option to transfer to Talktalk as they used to run the landline service for Sainsbury's. I imagine the mobile customers were able to transfer to the other network in pretty much the same way and get credits refunded.