Imo is already known for their instant messaging aggregator that combines 11 of the most popular services into one. The app even supports free VoIP calling for Android users but now the company is introducing the same calling feature for iOS users. The app requires iOS 3.1 or higher and a 3G, 4G or Wi-Fi connection to work.

When operating over a 3G or 4G connection, the service will naturally eat into your data plan but that can be eliminated by switching to a Wi-Fi connection. Call quality, according to Imo, is just as good as a standard phone connection without having to use any of your minutes.

The multi-function app also combines multiple IM networks into one, including Facebook Chat, Google talk, Skype, MSN, ICQ/AIM, Yahoo, Jabber, Hyves, VKontakte, Myspace and Steam. The service additionally supports group messaging, photo sharing and voice IMs that essentially turn your phone into a walkie-talkie. There’s even a searchable chat history for keeping a record of your conversations.

Imo has emerged as one of the top chat aggregators with more than 4 million mobile downloads and 700,000 daily users that deliver an average of 50 million messages each day.

The free voice calling feature became available to Android users back in February although we are unsure why it took so much longer to arrive on iOS. But as TechCrunch notes, Imo is a bit late to the party as there are already several other alternatives like Viber and Nimbuzz that offer free iOS calling.