GPT 4 and GPT-4o are available for use in voice conversations. GPT-4o mini is not available for voice conversations.
Keep in mind that GPT-4 and GPT-4o have message limits for Plus and Team plans. For users on the Enterprise plan, there is no message cap.
GPT-4o real-time voice and vision will be rolling out to a limited Alpha for ChatGPT Plus users in a few weeks. It will be widely available for ChatGPT Plus users over the coming months.