Vodafone currently offers two kinds of deals, one for PC tethering and one for small screen browsing.

1. PC Tethering

In December 2008, Vodafone started their 'TopUp and Go Mobile Broandband' offer. The package costs 39 pounds and includes a 3G dongle, a SIM card and 1 GB worth of data traffic. The Vodafone web site states that there is no time limit in which 1 GB has to be used ("No time pressure – your TopUp won’t run out after 30 days").

It seems that the SIM card can also be used in another 3G dongle (in case you already have one) and this thread in the Vodafone customer forums suggests the original software might not be necessary either.

Every additional 1 GB costs 15 pounds. Top-up works via vouchers (not quite clear to me how to use the vouchers without the Vodafone software) or by calling 08080-101238 and using your credit card (not sure if international credit cards work, to be verified).

According to the thread above the connection details are as follows if you use the SIM without the Vodafone software:

• APN: pp.internet
• Username/password: not necessary
  

2. Small Screen Web Browsing

On Prepaid SIM cards, Vodafone UK offers mobile phone web browsing with a cap of 0.5 pounds (50 pence) a day for a maximum of 25MB. This web page mentions that if more is consumed they "will be in touch". They don't say exactly what that means.

Tested services:

• Web browsing with the Nokia browser
• Web browsing with Opera Mini
• eMail via POP3, SMTP
• Nokia A-GPS lookups (with a Nokia N95)
  

Tethering with the PC is not allowed as per the fine print. It is nevertheless be possible.

Tech Details:

• APN: pp.vodafone.co.uk
• Username and password (not sure if that is necessary): wap / wap
• To check balance: *#1345#
• To get you own number: *#100#
  

Misc Info:

• Price of the SIM: 5 pounds, with 1 pound of balance on the SIM

• The 50 pence a day option for Internet access comes by default, activating an option is not possible

• TopUp/charge can be done by credit cards via vodafone's web site, but some cards issued outside UK may not be accepted. As of Feb 2009. Japanese credit cards could not be used.

• TopUps can also be bought in Vodafone stores. It's not necessary to know your mobile phone number.

• Starting 1. July 2009, Vodafone has new data roaming prices that might be interesting for some applications. More details here. Unfortunately, the page does not say if the offer can be used with a prepaid SIM and how mobile phones and PCs, for which pricing is different, are separated.