For each mobile operator in the UK, I want to know:
- Which high-speed data mobile plan offered by that operator would be
cheapest for a customer who only uses the phone for data transfer, and
who transfers 2.5Gb per month?
- What are the specifics of this plan? (Monthly fee, minutes, cost per
Mb data transfer, minimum contract period, etc.)
- Does this plan require the customer to buy a handset from the
operator?  If yes, what is the cheapest plan that _doesn't_ require
this? What are the specifics of that plan?
- Is/are this/these plan(s) available everywhere/to everyone in the
UK?  If not, what are the limitations?

By "high-speed mobile data" I mean mobile data services with at least
100kb/s download rates.  This includes all 3G services, as well as
GSM-EDGE and equivalent technologies.