theres no limit as such, but they will warn you when you are using way to much
This is in place to stop people using their phone as a modem for their laptop.
details.......
Quote:
“Our new O2 Web Bolt On gives you unlimited browsing for just £7.50 a month.
To opt into this Bolt On simply send a free text message with the keyword WEB to 21300 or call free on 2425 from your mobile.
Paying for your Bolt On is simple as it comes out of your calltime balance each month. We do all the work, all you have to do is keep your mobile topped up with enough calltime credit to pay for your calltime and your Bolt On payment each month.
Each month, we will send you a text message to let you know 48 hours before we are due to take the next months payment giving you a chance to top up your calltime balance to pay for your Bolt On or to opt out or change your choice.
You can opt out up to 48 hours before the next payment is due simply by sending a free text message with the keyword WEB OFF or by calling 2425 free from your mobile.
The O2 Web Bolt On can only be used for internet browsing on your phone. A fair use policy applies and if your usage substantially exceeds that of other users, which is normally expected to be below 200MB/month, you will be charged standard rates for additional browsing. We will send you a warning text message advising you to limit your usage before this occurs and a text message to confirm when you are being charged”