I don't know about the charge but talk to BT. Be very wary of Tiscali, I am always careful about putting all my eggs in one basket if something goes wrong then you will be without three services. Tiscali have a track record of offering the earth just to hook you in - think of the Nationwide advert and then basically giving you the worst service of any ISP I have used.
I personally would never consider this type of package when you see an offer that sounds too good to be true - it usually is.