You could upgrade to the VIP Package, that includes free local and national calls and discounted rates to mobiles and international numbers (...and V+ box, V Box, XL TV and XL Broadband) for only £85/month:
http://allyours.virginmedia.com/webs...ct.do?id=11029
Canceling depends on whether you're still in your contact period. If you are, you'll have to buy yourself out (expensive), if not I don't know how long it'll be before VM will let you reconnect.
Bear in mind that Sky's broadband is ADSL, delivered down copper pipes and in all probability won't be the speed you pay for. With VM you stand a better chance of getting full speed (you must have seen the massive ad campaign?)