Might be worth noting that T-Mobile and O2 (my current and previous contracts) also state that you can't use them as bluetooth modems for laptops/PCs (not sure on the exact wording but that is the general gist because they want ot to pay for the mobile broadband instead) yet with both contracts for the last 3 years I have use my mobiles as BT modems with various laptops using absolutely loads of data, especially on the T-Mobile contract (I remember looking at my usage once on my N70 and my total Down was at least 3GB at one point (though not sure over what time period - it was a while back!). And I never heard a thing from them, never got charged any extra nothing. So unless the physically block a particular port for Skype, you might get away with it.

Disclaimer: If you do it and get caught it's not my fault!