In reply to blanchie14c:
I just bought one on 3 from nearest supermarket to the site I was working on. Cost £40 with 3Gb of credit. Most of the providers will have cost per minute on their websites. Credit was put on via internet portal or by voucher.
GiffGaff have a list of prices for mobile data on their site and gives examples of what 500Mb, 1Gb etc mean in real terms - Usage info should be roughly the same for everyone.
I was sending quite a few large docs, on the e-mails for 4 days and one of the managers stole it to use to make an internet call and not used up all the credit yet.
Cheers,
Stuart