Do I need a Zendesk Talk subscription to use Zendesk Sell Voice?
No, Zendesk Talk and Zendesk Sell Voice are two different in-product telephony features. Zendesk Talk is a cloud-based call center software that is built into Zendesk Support. While Zendesk Sell Voice is a cloud-based calling software that is built into Zendesk Sell.
For more information, see the article: Enabling Sell Voice.