Re: 1, Sainsbury's Mobile is an MVNO on Vodafone, and Virgin is an MVNO on EE, so strictly speaking that's correct (see my previous answer here about how it's probably getting this info: https://news.ycombinator.com/item?id=9300690)

Re: 2, the data is available from Ofcom - maybe if you ask Twilio nicely they'll load it :)