Just had a text message from Virgin which says:

"From 28/04/08 mins and txts will not rollover. From 23/06/08 mobile
internet in the UK will cost 0.2p/Kb, not 0.5p. See
virginmobilepeople.com/300300 or call 789"

The http://www.virginmobilepeople.com/300300 page talks about the tariff
costing £10 but I presume this is aimed at those on the package who also
have Virgin Media broadband/TV/phone lines at home because I've always
paid £15 for this package.