I found this the other day
www.teamspeak.com wouldn't work for me or another friend on virgin, I powered off my router for a bit when I was laying some cat5 around the house and then I could access it again, only thing that had changed was my ip onto another range so im guessing they had blocked that range.
That's one of the problems with dynamic IP, you often inherit the bad reputation of someone else who has used that range. What's worse is that in today's age of always on connection's there's no need for dynamic IP as an ISP needs to have enough IP's to go around. Its actually harder to run a dynamic IP pool's for that many users than it would be to statically assign a single IP to each customer.