I now have BT4600 with answer phone feature enabled. I’m greatly confused about the BT feature range so this is probably a question with an obvious answer. Should I now cancel Voicemail, or whatever the facility it is that lets me use 1571 to hear missed messages?
I see no explicit mention on the list in myBT of ‘1571’ and nor can I find any consistent documentation about it.
You can if you wish but there's nothing to say you have to.
On the one hand 1571 may answer before your BT4600 does (depending on how many rings you set the 4600 to answer after). On the other hand BT are moving toward Digital Voice which comes with 1571 included at no extra cost