Repeat both at least twice during your voicemail. With regards to your telephone number, pauses in your speech will give your listener a chance to catch up and not miss any details. For example, say your telephone number this way “1-2-3- pause -4-5-6- pause -7-8- pause -9-10″. If you need to leave an email address, spell it out.
Assuming you have a strong 1st attempt voicemail message, when on your 2nd attempt should you get voicemail again, simply lead with:

It is no surprise that your actual voice mail greeting must be delivered in the same way: Professional, clear, brief, and to the point. In a previous blog, "Marketing Messages on Your Cell Say You Mean Business," some techniques for making a professional voice mail greeting were discussed. There are many similarities between leaving a voice mail, and producing a voice mail greeting. You want your callers and receivers to hear a confident and professional person on the other end delivering a coherent message. You should introduce yourself to a prospective client in a personal way. An email doesn't generate much discussion, nor does it necessarily show you went the extra mile in contacting the client. Generating conversation. A professional, well conveyed voice message shows the voice mail receiver that you are confident and well-spoken, and that there is a person behind the message. Emails can be prepared, edited, and revised unlike voice mail messages An email or email chain thread is documentation of a conversation that can easily be referenced In an email you can include a phone number, address, website, etc that may be hard to remember or record through voice mail communication Emails can be forwarded, CC'ed, and blasted.
If your Android phone doesn't have the Google Voice app, go to Google Play Store and search for it to install it on your device. Once installed, launch the app, and go to the "Menu" at the top left, and select "Settings." Then, go to the "Voicemail" section and tap on the "Voicemail greeting."