Looking at hosting one box (maybe 2 in the future). At the moment I haven't talked to the customer enough to find how much traffic we're looking at, but somewhere between 50-100 GB a month max I'd have thought, possibly less.
Being located in the UK (particularly london) would be particularly useful, although I'm willing to consider other options.
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EDIT: Dedicated hosting may also be possible, depending on how much flexibility we get...