Imo offers free voice calling for iOS users

The imo instant messenger app has been updated to add voice calls. The app can communicate with your friends on any almost IM network, including Facebook Chat, Google Talk, Skype, MSN, ICQ/AIM and more. With this latest update the app adds high quality voice calls.

To place a call, you tap a contact's name, and you are connected. Callers can contact other imo users on iOS or on Android. There's a video tutorial on the web.

imo requires a sign up, either through imo, or it can work with one of your existing social network logins. The app works on the iPhone and iPod touch and requires iOS 3.1 or later. There is a separate iPad app but the newest voice feature has not yet been offered for the iPad.

imo has a good following and generally positive reviews. This update should add to its popularity.