________ allows standard telephone users to easily initiate calls to TTY users.

The correct answer is Voice to Relay, which refers to a service that enables standard telephone users to communicate with TTY users through a relay service. In this context, the term "voice" signifies the ability of a standard phone user to initiate a call and have their spoken words converted into text by a relay operator, thereby allowing for effective communication with someone using a TTY device.

When someone calls a TTY user from a standard telephone, the relay service plays a crucial role. The operator who monitors the conversation translates voice to text, allowing the TTY user to read the conversation. This process is essential as it ensures that individuals with hearing impairments can communicate as easily as those without disabilities.

Other options like Text Relay or TTY Interface pertain to different aspects of telecommunications for the hearing-impaired but do not specifically describe the process by which standard phone users initiate communication with TTY users. Video Relay pertains to sign language interpretation and is also not applicable in this context. Therefore, Voice to Relay is the most fitting choice as it encapsulates the functionality needed for standard telephone users to connect with TTY users effectively.