I have used this app since day one and shared it with everyone I know. It is probably my utter most appreciated app in either Apple/Android market and I use it ALL THE TIIIIIIIIIIME.
This app is both free and functional allowing you to send short voice messages to people instead of either talking on the phone or using annoying teeny weeny keyboards to type a text. For someone like me who is one of the last 4 people without unlimited texts and hate using them this allows me to send that sentence in a quick tap/record and wait for a response. It removes the need to actually dial someone so you both avoid interrupting them and not having to have a full fledged conversation if you don't want to. Some may say "ohhh you means it's nextel?!" NO! NO! It's not Nextel by any means. This app saves each message until you delete them so it allows you to go back into a conversation and relisten to messages and even forward them.
The ONLY con I have found is it's account profile setup. You create an account by creating a contact for yourself in your phone list. Doesn't sound to bad but if you redo your phone your account is no longer valid to the APP, EVEN if your using the same name. If you fear being bothered by strangers and keep your security up then you have to reinvite every one of your contacts back into your profile. I have found that by setting the security to low you no longer have to invite people BUT most times if you dont contact them first and they try to send you a message it wont work since your old account is basically void. Worse off they wont know since it will appear on their end the chat goes through. So every time I have to redo my phone I have to go through my main people and send a quick "hello" just so I will refresh in their list.
Other than that though this app is AWSOME. Create an online user profile storage like KIK Messenger and it would be Omega!