I recently ported my number to 2talk and it proved an easy and painless experience. Already using a VOIP and VDSL capable router so now, for $11.50 I get 250 mins free with a national and country package, which, for someone with an English wife and numerous friends gained from 30+years living in Europe is a useful saving, made more so by the fact that a call just down the road to Christchurch is a toll. In a couple of days I will, hopefully, have a naked VDSL connection and Sky with Vodafone at $65 (with on account discount) for 80Gb and free MySky. So $76/month for phone, VDSL and a further $15 saving with free MySky, compared to $95 for phone +VDSL if I stayed with current ISP.
I seriously looked at Vodafone but as I "own" my MySky HD, having paid a one-off cost many years ago, that was no benefit and they wouldn't give any credit for it. W Nation has a ridiculously large 2000 minutes/month call allowance.