I recently discovered a tool called SpeakPipe which allows readers of your blog to send you a voice message. Messages will show up in your SpeakPipe account, and you will also receive an email message when you receive a voice message in the email that you set up on your SpeakPipe account.
The free plan allows you to have 20 messages per month, of a maximum duration of 90 seconds each.
Just embed the code in an HTML widget on your blog and you are good to go. Directions are here. You will see a tab on the right side of your blog that says, Send Voicemail. Users just click record and send. Check it out by clicking on the tab to the right, or you can do a test at speakpipe.com.