... it actually isn't as bad as I feared when I saw the dreaded * next to the word 'unlimited', but if you scroll down you get...

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Our fair use policy

We have fair use limits and hope you’ll use your common sense. These limits should be big enough for you to do all the things you want to do. But we’ll get in touch with you if we think you’re using our services unfairly, and especially if you’re abusing them. If we find people are using X-Series above these limits, we’ll review them. Here’s our take on fair use:

• Unlimited data is 1GB per month. Also, your data usage doesn’t include using your mobile as a modem.
• Windows Live Messenger won’t count towards your monthly data fair use limit but has its own limit of 10,000 messages per month.
• Skype on 3 is 5,000 minutes per month. If you go over this you’ll need to wait until the start of the next bill month for the service to resume, however Skype calls can still be received.
• Orb and Slingbox have a total combined limit of 80 hours a month.

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To be honest that really IS plenty.  I doubt I watch 80 hours of programs on my regular TV let alone my slingbox!  I may just jack off my Orange contract get an N73 and do this.....