Pockets is a very, very cool little application. You are able to leave a voicemail for anyone with a Twitter id, they get an @ message they have a voicemail and can then click the link to authenticate and receive the message! They can even reply.
Now I tried to sign in, and it uses oAuth, but it would not pass me over to Twitter to authorize the service for testing. I will do a browser restart and give it another shot. But in the help video on their site, they show an example of the service sending a tweet with the voicemail link, playing your voicemail and even sending a reply. The service calls your phone for you to record the messages.
The UI was clean and slick. I am not sure where the monetization comes in, maybe a brief ad later for non-paid accounts. But for now, it is free and works well.