I have the same one... 10 quid for 1GB which you can use for a month.. when the month is up.. used or not and you ahve to buy more... but the good thing for me (prob not you) is that you can go a couple of months without using it.. you dont have to top up every month
1 gig is enough for email and accyweb and looking at a few sites.. stay away from sites that have a lot of pictures to view..
you can check in your 3 control panel what your using a day
keep to text based stuff and your OK ..1gb or 250MB a week or less than 50mb a day .. should be ok for light use
I use mine for sending pictures to the papers when at away games midweek
