Seems pretty paltry, especially as it's for phone only customers and line rental is already overpriced. Freezing a high price is only a good deal if it stays frozen for a few years.
BT offer a £5.10 per month offer for people on certain benefits, which luckily my 90 year old gran qualifies for. For an extra £5 a month she also gets broadband. Plus BT actually have a team of people dedicated to their older customers, so they dont have to deal with offshore agents and they are great when dealing with grandkids who are helping out