Android phones can access voicemail by holding down the 1 key on the dial pad until the phone dials your 10-digit phone number. You will automatically connect to your mailbox and be prompted to enter your temporary password; this password is the last 4 digits of your phone number followed by the # key. How do I check my voice mail? To call your voicemail on an Android phone, simply open your phone’s dial pad and hold your finger down on the “1” key. You can also call your voicemail from a different phone by calling your own number and tapping the pound key. How do you listen to voicemail on this phone? Turn on your phone and open the Phone app. Call your voicemail system. Enter your voicemail system passcode. Tap the key that allows you to check messages. Listen to each message and tap the corresponding key to replay it, delete it, or save it. How do I get my voice messages from this phone?
Since leaving your first voicemail message that was followed by a proper corresponding email, did you also look them up on LinkedIn and send a connection request?

A sales voicemail is no time to lock into the technical specs of your product or service. You can't take it as an opportunity to describe the nuances of how all of its features work — complete with confusing, technical jargon and long-winded detail.
Clearly state your purpose and next steps. Whether it’s a demo, an appointment, or the best contact to talk to, simply ask for it.