I have been using Magenet for about a year now. The package we have combines 4 MB download speed with free phonecalls (for up 1 hour) to local and national landlines.
There were some problems initially, the main one being that if I was downloading an mp3, it was very diffult to have a phone conversation. We could hear what the caller was saying but the caller could barely hear us. Eventually, after a number of visits from service engineers, the problem was fixed after about 2-3 months.
Overall, we have found the sevice to be good value.
However, we are thinking of switching to the 3 MB package from BT ireland because even though the contention ratio is greater, it will allow us to make free phonecalls to local, national and UK landlines.