Google voice : Personalized Greetings :

Customize voicemail greetings and settings

With Google Voice you can record one voicemail greeting for everyone who calls or you can have different voicemail greetings based on who's calling.

Record a custom greeting for all callers

1. Go to Google Voice.
2. Click the gear icon at the top right of the Google Voice window and select Settings.
3. Click the Voicemail & Text tab.
4. In the 'Voicemail Greeting' section, click Record New Greeting.
5. Enter the name for the greeting you're going to record and click Continue.
6. A "Record Greeting" box will appear. Select one of your forwarding phones from the "Phone to ring" drop-down menu. 
7. Click Connect.
8. Google Voice will call you on the forwarding phone you selected. Pick up the call and  record your voicemail greeting when prompted.
9. Once you've recorded your voicemail greeting, make sure it's selected in the 'Voicemail Greeting' section of your Settings.
10. Click Save changes at the bottom of the page.

If you'd like specific contact groups or individuals to hear another custom greeting, you can record different greetings. For example, you can record specific greetings for your parents, your colleagues, and your best friends.  

Choose a setting to customize greetings for a group, a specific person, and call screening:

Record a custom greeting for a group

To record a custom voicemail greeting for a specific contact group:

1. Click the gear icon at the top right of any page to access your Settings.
2. Select the Groups & Circles tab.
3. Click the Edit button under the group you want to record a custom greeting for.
4. Click the Record new button in the "When people in this group go to voicemail" section.
5. Enter the name for the greeting you're going to record and click OK.
6. A "Record Greeting" box will appear. Select one of your forwarding phones from the "Phone to ring" drop-down menu. 
7. Click Connect.
8. Google Voice will call you on the forwarding phone you selected. Pick up the call and  record your voicemail greeting when prompted.
9. Pick up the call and record your voicemail greeting when prompted.
10. Once you've recorded your voicemail greeting, make sure the voicemail greeting you want to play is selected from the "When people in this group go to voicemail" section.
11. Click Save.

Record a custom greeting for an individual

To record a custom voicemail greeting for a specific contact:

1. Go to Google Voice. 
2. Click the History tab.
3. Scroll to the contact name for the custom greeting, and click the contact's name.
4. Click Use phone to record a new greeting.
5. Enter the name for the greeting you're going to record and click Continue.
6. A Record Greeting box appears. Select the phone you want to call to record the greeting, from the Phone to ring drop-down menu.
7. Click Connect to ring your selected phone.
8. Pick up the call and record your voicemail greeting when prompted to do so.
9. Once you've recorded your voicemail greeting, make sure the voicemail greeting you want to play is selected in the drop-down under 'When this contact goes to voicemail' section for the specific contact.
10. Click Save.

Record name for call screening

To record a custom voicemail greeting for a specific contact:

1. Go to Google Voice. 
2. Click the History tab.
3. Scroll to the contact name for the custom greeting, and click the contact's name.
4. Click Use phone to record a new greeting.
5. Enter the name for the greeting you're going to record and click Continue.
6. A Record Greeting box appears. Select the phone you want to call to record the greeting, from the Phone to ring drop-down menu.
7. Click Connect to ring your selected phone.
8. Pick up the call and record your voicemail greeting when prompted to do so.
9. Once you've recorded your voicemail greeting, make sure the voicemail greeting you want to play is selected in the drop-down under 'When this contact goes to voicemail' section for the specific contact.
10. Click Save.

Via : https://support.google.com/voice/answer/115069