I have been with the post office for about two years now, never had a problem with them, my sky tv still works with them, and my broadband does as well - even though both state I must have a BT line.
The only thing that i didn't like about the post office is the minimum monthly payment you could make was £15 a month, we hardly use our phone for phone calls as me and my husband both have mobiles, so most of the time our bill is just line rental. They do however let you pay the full amount every three months by dd.
Hope this helps.
Claire