https://windowsphone.uservoice.com/forums/101801-feature-suggestions/suggestions/3723135-blutooth-auto-answer-on-windows-phone

I am a traveling sales person and I need auto answering feature on windows phone while driving.

No it is not Peter/David,
automatic call answer is not available on all Lumia Smartphones.

If you would like to have this feature, please Vote for it at this Microsoft Site:

https://windowsphone.uservoice.com/forums/101801-feature-suggestions/suggestions/3723135-blutooth-auto-answer-on-windows-phone

Yes, Peter, automatic call answer is available as a feature and you can enable it through the phone's Settings menu. The Nokia Lumia 925 can answer calls automatically as long as certain accessories are connected to it (i.e. via Bluetooth, such as a BT headset).