ok, so, broadbamd first. Unless you are on virgin/cable your speed will be limited by how far you are from the exchange. More than a mile and you will not be getting the full 8/16 mb advertised. Also, depending on what you use your connection for the upload speed may be important, most isp's limit this to 1/2 a meg, tho you can get different connections which are greater, but with a lwer downstream speed as a result. The 16mb from sky depends on if your exchange has let sky fiddle as if not, the max will still be 8meg. Sky had a lot of bad press regarding their service, but this is normally down to the firmware they put on their routers, you can replace this and fix that issue, they have alsobeen known to give high latency, which will mean online gaming is not really usable and webpages ttake ages to load, a call to them fixes this. if you are with bt, when they change their broadband service soonish, you will have to pay a high premium to reserve bandwidth, otherwise you'll get left with the dregs, reading up on what they're proposing, its outrageous.
Sky hd. Watch a sky channel that also broadcasts in hd, example sky movies, then flick to something like discovery or even bbc, notice a difference? Sky deliberately broadcat these channels in a lower qualitry, including sound in order to convince people they need hd, for this reason alone i wouldn't get it. Also, noticed how good their add for hd looks? Why dont they broadcast all shows in that quality? Besides all that, there just aren't enough channels yet. I'd say your money is better spent on a blu ray player or ps3. Oh and the sky hd isn't full hd, so it wont be 4 times the detail.
Phone wise, the best deal i found is the sky talk, for £5, i get unlimited calls 24 7, to all uk, and a load of worldwide destinations, keeps the wife happy during the day, as she dont have to wait till after 6 now.
Hope this helps, any questions just ask!!!