I could write a program for when you speak it will save the file then cut it into 100s of parts along with a file then you can send it to your contact and with the program it will read the text file and put it back together so he/she can listen to it.
It not really what you wanted but i will give it a try and might not work plus you will both have to have the program and i will make things slower ( you will have to recored then save the encode then save again then send then .......)
Adeptus's idea is the best shurly!
http://www.google.co.uk/search?hl=en&safe=off&sa=...voice+talk&spell=1
I searched google and there is alot of good ones and there encrpted!